. Is it possible?

Yes. See the documentation on how to start a process.

I need to cancel the process and continue it from the dialog several time because it is a long process.

Did you try kill()/terminate()? Did you verify when your clicked slot is getting called as I mentioned a couple of times? I don't know what there is not to understand, if you want to kill a process on a click then just do so.

I need to cancel the process and continue it from the dialog several time because it is a long process.
I could send a code it is necessary, but it did not work.

When I clicked the cancel button, It seems the signal is emited once the process is finished, but I want to be able to cancel the operation in the middle of the process.

Don't know what you're seeing. What signal, that for the click? Unless your computer is very busy running the other process so it doesn't service the request promptly. Start with a qDebug() in your clicked handler so you know when it's called.

Note that your dialog->show() means it's (presumably) a modeless dialog (oh, actually your title says you have set it modal). You still have to allow the event loop to run. Can't tell from your code, but if your while (bExec) blocks the event loop that might be a problem. Like I said, start by verifying how promptly you get the clicked signal.

Ah, hang on:

cancel slot:
//update bool exec to false

Just updating bExec to exit the while loop is not enough to kill the spawned process. And I don't know what your while (bExec) is looping on if you have spawned a sub-process.

Sorry, I did not explain it very well.
The question I have is I want to run a process in background and at the same time, I should be able to stop it from a dialog . Is it possible?

I do not have a code because I am not sure how to do it. I was thinking in use a thread. Could you give me some details to implement it?

Thanks.

void Run(bool bExec)
{

while (bExec)
{
///Execute process
}
}

main:
//setup dialog
//connect dialog button clicked to slot cancel
dialog->show();

cancel slot:
//update bool exec to false

user should be able to cancel the process by clicking the cancel button