openCV import error on python virtual environment

I have created a python3.6 virtual environment.When I import cv2 in terminal,it raise a exception which says ModuleNotFoundError:No module named ‘cv2’,but it works in real python3.6 environment.
Does anyone know the reason and how can I solve this problem?

Hi,

Please remember to enable the host side package to the virtual environment.

$ virtualenv env --system-site-packages
created virtual environment CPython3.6.9.final.0-64 in 433ms
  creator CPython3Posix(dest=/home/nvidia/env, clear=False, global=True)
  seeder FromAppData(download=False, pip=bundle, setuptools=bundle, wheel=bundle, via=copy, app_data_dir=/home/nvidia/.local/share/virtualenv)
    added seed packages: pip==20.2.1, setuptools==49.2.1, wheel==0.34.2
  activators BashActivator,CShellActivator,FishActivator,PowerShellActivator,PythonActivator,XonshActivator
$ source env/bin/activate
(env) nvidia@xavier8G:~$ python3 
Python 3.6.9 (default, Jul 17 2020, 12:50:27) 
[GCC 8.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import cv2

Thanks.

@AastaLLL
Thanks for your reply,it works