I tried to run a python script which does not exist in current folder, for example

C:\>python Test.py

python:can't open file 'Test.py':[Errno2] No such file or directory

I have to specify the absolute path c:\testdir\test.py to make the command workable.

c:\python c:\testdir\Test.py

I tried to append "c:\testdir" into Env argument 'PATH', but it still doesn't work.

i want to use the filename rather than the entire path, c:\python Test.py can i make it happen?

That means you're not currently in C:/testdir (you're in C:). Enter cd C:\testdir in your terminal to move to that directory (cd = change directory).

The reason you have to specify the entire path while out of the folder is because even if you're not in the folder that you're trying to reference, you can still use its path to reference it.