I have downloaded odoo9 source code from https://www.github.com/odoo/odoo --depth 1 --branch 9.0 --single-branch .
 and started the odoo server but i see "ImportError: No module named werkzeug.utils" error.
I tried installing with 
sudo apt-get install -y python3-werkzeug and could see it is installed successfully.
Again when I run the server I still see the same import issue.
how could I fix this import errors when I already installed them.
Odoo 9.0 is no longer supported since long ago, and it only works with Python 2, so you'd have to install python2-werkzeug instead (if available).
Only Odoo 11.0 and newer run under Python 3.
ImportError: No module named werkzeug.utils