I finally solved this problem。The trick is in Path system variable。First you should add C:\Users\xxx.rhinocode\py39-rh8\Scripts to Path ,Second,You must check if there exists another “scripts” path for another previously installed Python。If so , the program will import twice, resulting in a circular import。In my case, I previously installed Python3.8,so threre’s another “D:\Programs\Python\Python38\Scripts”,After I deleted this item, the import runs smoothly。I think Rhino should solve this, those who use Cpython in rhino usually installs another Python somewhere else on the computer, They can all run into this problem.