I want know how to go to china university of petroleum from beijing airport.

Do you refer to the Capital Airport?
If yes, you can take airport shuttle bus line 6, get off at Olympic Village. Then take subway line 8 to Zhuxinzhuang Station and take subway Changping Line to Nanshao Station, Exit B2. After that, take a taxi to your university directly. The cab fare is CNY 20 to 30 in the day time.