The CFM56-5B turbofan engine was discussed in this paper, functional model of engine control system and the control circuit's external interface were defined through requirement analysis. It proposed basic modeling principle of simulation of engine control circuit. Then the conditional directed graph theory combined with assemblies modeling method was adopted to establish engine control circuit simulation model. Finally, MATLAB/Simulink was used to simulate the component model of engine control circuit. And the results show that the simulation models are accorded with the requirements of simulator engine control system through adjusting and proving.