Deploying to Heroku: ImportError:Couldn't import Django

my StackOverflow friends,

When I want to deploy my code to Heroku using git push heroku master I have ImportError:Couldn't import Django. So I try python manage.py runserver to see what is going on and it shows this in the terminal. Full description of ImportError:Couldn't import Django. Before I tab all the process for deploying my code to Heroku,python manage.py runserver works well (the system gives me a link to open my Web page).

I am very new in PyCharm and Heroku and I do not know what is going on. I read a little bit about virtualenv, but I still do not know what is that. If you can help me, please tell me in details what should I do in basic programming language.

Thank you so much :)