QCoreApplication enters its event loop when you run a.exec(), and the application keeps running nonstop. When you click "X," the OS tries to terminate xterm by sending a termination signal. When xterm quits, it finds that you have a running program, so it pops that dialog to tell you that it has to terminate that program because the OS wants it to. It's not a problem, and you can ignore it.

I don't have your problem with Terminal.app either building applications in debug or release mode using a custom-built Qt 4.7.4 with Qt Creator 2.3.0 (on Mac OS X 10.7.1). The content in your first window is correct, obviously. But Qt Creator tries to launch some other things in your case. Sorry, but I'm as much in the dark as you are.

bring this error when using "/usr/X11/bin/xterm -e"

1:====when I put in "/Applications/Utilities/Terminal.app",
and then run debug model,it appear 4 terminal window:
1).
Last login: Wed Sep 21 15:34:38 on ttys002
rene-mac:~ mike$ /Volumes/Mac_OS_4/test/test/test ; exit;
hello

2).
Last login: Wed Sep 21 15:34:38 on ttys001
rene-mac:~ mike$ /Volumes/Mac_OS_4/test/test ; exit;
-bash: /Volumes/Mac_OS_4/test/test: is a directory
logout

[Process completed]

3).
Last login: Wed Sep 21 15:34:38 on ttys000
rene-mac:~ mike$ /var/folders/Vc/VcNYECwgEOuL5wCCeLqh1++++TI/-Tmp-/qt_temp.ux4229/stub-socket ; exit;
-bash: /var/folders/Vc/VcNYECwgEOuL5wCCeLqh1++++TI/-Tmp-/qt_temp.ux4229/stub-socket: Permission denied
logout

[Process completed]

4).
Last login: Wed Sep 21 15:34:11 on ttys003
rene-mac:~ mike$ /Users/mike/Qt/Qt\ Creator.app/Contents/Resources/qtcreator_process_stub ; exit;
This is an internal helper of Qt Creator. Do not run it manually.
logout

[Process completed]

it look like work well, but way happen to so much windows?

2:====when I put in "/usr/X11/bin/xterm -e",
and then run debug mode,it work well,
but when I try to close the window(click the "X" button at the left, top scope),
it appear a error dialog as below:
the inferior stopped because it received a signal from the Operating system.

Signal name: SIGHUP
Signal meaning: Hangup

My code is so simple:
@
//main.cpp
#include <QtCore/QCoreApplication>

int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);

printf("hello\n");
return a.exec();

}
@

when I try to comment some statement, as result below:
@
//QCoreApplication a(argc, argv);

printf("hello\n");
return 0;
//return a.exec();

@

it work well and the error dialog will never appear

My test.pro file is:
@
QT += core
QT -= gui

TARGET = test
CONFIG += console
CONFIG -= app_bundle

TEMPLATE = app

SOURCES += main.cpp
@

how can I resolve this problem?

By the way, Mac OS X does have xterm built-in, just not in its default PATH. Using
@/usr/X11/bin/xterm -e@
also works (by launching the X11 terminal).

I have considered filing a bug [bugreports.qt.nokia.com] report against the Qt SDK,

and fixed my problem under your suggestion: install xterm.
After installing, I configure "Tools->Options->Environment":
form "xterm -e" as default,
to "/usr/local/xterm -e".

BTW, how to configure Qt Creator to use the Mac terminal in Tools->Options->Environment?

I have tried "sh -e", "ash -e", "bash -e", but all are invalid.

I wonder why the later had not happened in the image. You might want to consider "filing a bug":http://bugreports.qt.nokia.com/ report against the Qt SDK to get that fixed in the next version.