Just now I tested GuiXT with the testkey, but I couldn't find the button "Activate GuiXT" in the status screen of the SAP system. Would you like tell me what happened with it, thanks a lot. I attach a screen shot of my GuiXT profile where I entered the testkey.

Going by the GuiXT profile that you sent, the problem is caused by the fact that you have entered an IP-number in "Enabled systems". Please remove it, or enter your system name, e.g. CQT into this field.
(If you leave this field blank, GuiXT is active for all SAP systems; otherwise GuiXT interprets this as a list of SAP system names.)

Then logoff and logon again and the "Activate GuiXT" button should appear.