Thank you, NyAw. I got what you mean. Just as you said here:

Quote Originally Posted by ^NyAw^ View Post
I'm telling you that you can create the variable when you install the application on another system. It's so easy.
.
I can create the env variable to save the Qt's installation directory in my installation program, but the key point is: how to find out where the Qt installed?

My original meaning is, whether Qt provides a class/function to make it possible to check out the Qt's installation directory directly. If the answer is no, yes, this is not a Qt programming related problem.