Does any of the functions you call in your HelloThread_1 block ?

Not that it's not a good idea to have an infinite loop without a break condition to cleanly stop the thread.

am i correct ?

No, you are wrong. You just have to make sure you don't open too many files at once.

I ask now for the third (and last) time: for how long does your blocking function block?

not inside thread.

am i correct ?

thread 1 execute for only one time then it get block. while thread 2 run continuously

#include "dialog.h"
#include "ui_dialog.h"
#include <QDateTime>
#include <QDebug>

#include <QFile>
#include <QTextStream>

Dialog::Dialog(QWidget *parent)
    : QDialog(parent)
    , ui(new Ui::Dialog)
{
    ui->setupUi(this);

    StartThread();
    qDebug() << "End of Program";
}

void Dialog:: StartThread()
{
    HelloThread_1 thread1;
    HelloThread_2 thread2;

    thread1.start();
    qDebug() << "hello from GUI thread " << thread1.currentThreadId();


    thread2.start();
    qDebug() << "hello from GUI thread " << thread2.currentThreadId();
    thread1.wait();  // do not exit before the thread is completed!
    thread2.wait();  // do not exit before the thread is completed!


}


void HelloThread_1::run()
{
    while(1)
    {
        if(QThread::currentThread()->isInterruptionRequested())
            return;

        qDebug() << "hello from worker thread AAAA";

        FuelCheck ObjFuelCheck;
        
        ObjFuelCheck.gauge_init();
       
        int Percentage = -1;
        bool bisFuelConnected = true;

        ObjFuelCheck.gauge_cmd_read(ObjFuelCheck.nI2CId, 0x2c);
qDebug() << __LINE__;
        Percentage = ObjFuelCheck.u16Datareceived;

        qDebug()<< "percentage :"<<Percentage;

        QFile data("/home/user/output.txt");
        if (data.open(QFile::WriteOnly | QFile::Append | QFile::Text)) {
            QTextStream out(&data);
            out << "Result: "<< QDateTime::currentDateTime().toString("dd MMM yyyy HH:mm:ss") << " "<< "percentage :"<<Percentage<<"\n";
            // writes "Result: 3.14      2.7       "
        }

        QThread::msleep(100);
        if((Percentage < 0) && (Percentage > 100))
        {
            bisFuelConnected = false;

            qDebug() << "Fuel gauge found but wrong percentarge detected : " + QString::number(Percentage);
        }

        **// below  part block function **
        FuelGaugeProfileUpdate *pFuelGaugeProfileUpdate = new FuelGaugeProfileUpdate();

        if(IS_VALID_OBJ(pFuelGaugeProfileUpdate))
        {
           pFuelGaugeProfileUpdate->bIsRequiredToUpdateFuelGaugeProfile =true;
          
            if(pFuelGaugeProfileUpdate->bIsRequiredToUpdateFuelGaugeProfile)
            {

                pFuelGaugeProfileUpdate->show();
            }
            else
            {
               DELETE_OBJ(pFuelGaugeProfileUpdate);
            }

        }
        //------------------------------------------------
       NfcTagReaderWriter *objNFCTag_write = new NfcTagReaderWriter();

        if(IS_VALID_OBJ(objNFCTag_write))
        {
            if(objNFCTag_write->NFCInit())
            {
                if(objNFCTag_write->ReadNdefTextMessage() == 0x00)
                {
                    qDebug()<<"WriteNdefTextMessage";

                    QFile data("/home/user/output.txt");
                    if (data.open(QFile::WriteOnly | QFile::Append | QFile::Text)) {
                        QTextStream out(&data);
                        out << "Result: "<< QDateTime::currentDateTime().toString("dd MMM yyyy HH:mm:ss") << " "<< "objNFCTag_write->Text.text :"<<objNFCTag_write->Text.text<<"\n";
                        // writes "Result: 3.14      2.7       "
                    }
                    //objNFCTag_write->WriteNdefTextMessage();

                }
            }
            qDebug() << __LINE__;
            DELETE_OBJ(objNFCTag_write);
        }

qDebug() << __LINE__;
            QThread::msleep(1000);


    }
}


void HelloThread_2::run()
{
      while(1)
      {
          if(QThread::currentThread()->isInterruptionRequested())
              return;
           qDebug() << "hello from worker thread BBBB";

           ExtAdc  ObjExtAdc;
           AdcSettings AdcInfo;
           uint8_t u8ReadADC_no = 2;
           ObjExtAdc.AdcReadFile((ADC_type)(u8ReadADC_no));

           QString sADC_value = QString::number(ObjExtAdc.i32AdcReadValue);
           QFile data("/home/user/output.txt");
           if (data.open(QFile::WriteOnly | QFile::Append | QFile::Text)) {
               QTextStream out(&data);
               out << "Result: "<< QDateTime::currentDateTime().toString("dd MMM yyyy HH:mm:ss") << " "<< "u16AdcValue "<<sADC_value<<"\n";
               // writes "Result: 3.14      2.7       "
           }
           qDebug()<<"u16AdcValue "<<sADC_value;

           /*
           uint16_t u16AdcValue = 0;
           bool bIsVinVolt = false;
           float fVinVolt = 0.0;


           ObjExtAdc.GetAvgValue(ADC_BATTERYLEVEL);
           if(AdcInfo.bAdcReadError == true)
           {
            qDebug()<<"adc read error";
           }
           else
           {
               u16AdcValue = AdcInfo.u16AdcAverageValue[ADC_BATTERYLEVEL];

               QFile data("/home/user/output.txt");
               if (data.open(QFile::WriteOnly | QFile::Append | QFile::Text)) {
                   QTextStream out(&data);
                   out << "Result: "<< QDateTime::currentDateTime().toString("dd MMM yyyy HH:mm:ss") << " "<< "u16AdcValue "<<u16AdcValue<<"\n";
                   // writes "Result: 3.14      2.7       "
               }
               qDebug()<<"u16AdcValue "<<u16AdcValue;

               if(u16AdcValue < 11500)
               {
                   bIsVinVolt =false;
                   //TableInsertData(sBattery(), sLow()); // + " " + QString::number(u16AdcValue));


               }
               else
               {
                   bIsVinVolt =true;
                   //TableInsertData(sBattery() , sOk()); // + QString::number(u16AdcValue));

               }
           }
*/

              QThread::msleep(1000);

      }
}

Dialog::~Dialog()
{
    delete ui;
}

this is the main problem. and 2nd problem without comment my blocking function how to make this code get work simultaneously

can you elaborate your question more i am not understand your below question :
Does that function provide a way to interrupt it?

So what i need to change in above code to cleanly stop thread ?

https://doc.qt.io/qt-5/qthread.html#isInterruptionRequested

cleanly stop the thread.

So what i need to change in above code to cleanly stop thread ?

FuelGaugeProfileUpdate *pFuelGaugeProfileUpdate = new FuelGaugeProfileUpdate();
if(IS_VALID_OBJ(pFuelGaugeProfileUpdate))
{
pFuelGaugeProfileUpdate->bIsRequiredToUpdateFuelGaugeProfile =true;
if(pFuelGaugeProfileUpdate->bIsRequiredToUpdateFuelGaugeProfile)
{
pFuelGaugeProfileUpdate->show();
}
else
{
DELETE_OBJ(pFuelGaugeProfileUpdate);
}
}

Does any of the functions you call in your HelloThread_1 block ?

Not that it's not a good idea to have an infinite loop without a break condition to cleanly stop the thread.