In this paper, the significance of simulation research and analysis of air conditioning system (ACS) for civil aircraft are introduced. The mathematic models of ACS components for civil aircraft are built, and the simulation modules of ACS components and cabin/ cockpit heat load module are developed. The simulation model of air conditioning system for some civil aircraft is established, which is verified by examples. ACS ram air flow-rate calculation in flight envelope is predicted by validated simulation model . The ram air energy consumption is evaluated by standard algorithm to provide the basis for ACS design optimization. It is of great references for civil aircraft ACS design,optimization and airworthiness compliance verification.