Abstract: The trade studies should be accomplished during the early phases of the design and development of an environmental control system. The objective of the trade study is to assure that all state-of-the-art design approaches are considered, and that the design selected will provide the best combination of performance ,aircraft penalty,and life cycle cost. Comprehensive and timely analyses require the use of advanced computation method and program.This' paper is concerned with an application of optimal design on air-conditioning system for a fighter cabin.As an example, a turbine-fan colling system is considered.In the analysis,aircraft penalty expressed by additional, weight of the fuel resulted from the system is taken as object function provided that the comfortable requirements of the pilot are satisfied,Besides that,the emprei- cal formulas obtained from the test study of the heat load and the air distribution for a cabin have been adopted.Thus,the selection of the air-conditioning system parameters is optimized. The computation results show that the mathematical model presented and the Sequential Unconstrained Mimization Technique and the Simplex Method adopted in the paper are suitable for the optimal design of air-conditioning system.