Based on the second law of thermodynamics, minimum entropy generation analysis of aircraft environmental control is conducted using the multi-objective optimization method. To design takeoff, climb and supersonic cruise, and take entropy generation minimum as the objective function, an optimization model is established. In the optimization computation, influences of flow ratio of heat exchanger, mass flow of bleed air, pressure ratio of compressor and turbine on system entropy generation during different flight phases are analyzed. To overcome the conflict between design variables during different phases, a multi-objective optimization model is established with minimum entropy generations as different objective functions at the
design points. The Pareto optimal set is obtained using the NSGA-II algorithm, leading to an optimal scheme. Simulation shows validity of the proposed method.