Based on the characteristics of the ECS, pulse width-fuzzy control concept was put forward. Four models, pulse width regulating, PID control, fuzzy control and combined control, were established with Fuzzy and Simulink tool boxes in MATLAB. The difference between the temperatures of mixed flow and the objective and its change rate were the input in the fuzzy system, and the output, the control signal, was obtained by fuzzy reasoning. Rank skipping response characteristics of the four control methods were computed and analyzed with temperature rank skipping signal. A group of dynamic parameters were selected as the input data, by which dynamic response of the combined control model was simulated. The result showed that combined control system could solve the problem of temperature fluctuation in existing pulse width regulating system efficiently.