Terminal执行python manage.py runserver时报错

G:\Django项目\django_introduction>python manage.py runserver

Traceback (most recent call last):

  File "manage.py", line 10, in main

    from django.core.management import execute_from_command_line

ModuleNotFoundError: No module named 'django'

The above exception was the direct cause of the following exception:

Traceback (most recent call last):

  File "manage.py", line 21, in <module>

    main()

  File "manage.py", line 16, in main

    ) from exc

ImportError: Couldn't import Django. Are you sure it's installed and available on your PYTHONPATH environment variable? Did you forget

 to activate a virtual environment?

已经安装django了  总是报错  怎么破啊