Abstract: A mathematical model is developed for simulating transient performance of the turbofan engine,in which the transient heat transfer between the components and airflow,tip clearance and components efficiency changes caused by heat transfer are analyzed.The calculated result shows that there are significant influences of heat transfer on the engine's transient performance,and the component efficiency loss caused by tip clearance changes can not be ignored.The simulation accuracy can be improved by above model for the turbofan engine transient performance.