The heat pump air condition driven by biogas engine (BHPAC) is a new style air condition system,which is composed of the heat pump driven by biogas engine (BHP), the primary heat exchanger, the second heat exchanger, the water spraying chamber and other auxiliary equipment such as fans, water pumps etc. The mathematic model including the primary heat exchanger model, the second heat exchanger model, the water spraying chamber model, the mixed air model and the BHP model, was established to study the BHPAC system. The primary energy ratio for air condition was defined to evaluate the performance of the air condition. The results show that the air condition driven by biogas engine can save more energy than the heat pump air condition driven by electricity engine. The saving primary energy percentage for BHP is 75% in summer，and the saving primary energy percentage for BHP is 71% in winter. The BHP with the wet processing can be used in more areas than the common BHP.  