Oh! Thank you ,finally, I find the cause of the problem,firstly, I know the error is "Window can't find UCHTML\shell\open\command " , I believe the file is registry file , Secondly ,today ,I know that UC refers to a browser , so I think Maya think my default browser is UC browser , but I have not UC browser ,so Maya get me a error , then I download UC browser , as I said , Maya open help page in UC browser , Now I know have some wrong registry information refer to open html file by UC browser , I tried to change my default browser by modify registry , I went to HKEY_CLASSES_ROOT\http\shell\open\command->modify command 's default as google's path in my computer and went to HKEY_CLASSES_ROOT\http\shell\open\ddeexec\Application->change default'value is chrome , but it also can't work , so I think also have something more important I think I'm close to the answer , so I check it step by step , Eventually , I went to Computer\HKEY_CLASSES_ROOT\.htm and Computer\HKEY_CLASSES_ROOT\.html , change they're default value is ChromeHTML , then the problem is solved . god! Now I can open the Maya help page by F1 at last .