•Combining the ejector nozzle model with turbofan engine model.•A prediction method of infrared radiation intensity is proposed.•Combining the infrared radiation intensity prediction model with the engine model.•The overall engine performance changes under different mission stages are studied. In order to study the effect of ejector nozzle on the overall performance of turbofan engine, a turbofan engine model with ejector nozzle is established in this paper, which includes parameter cycle analysis module and performance cycle analysis module. A backward prediction method of infrared radiation intensity for exhaust system is proposed, which includes solid wall and gas infrared radiation intensity prediction. The infrared characteristics and overall performance of the turbofan engine with ejector nozzle are analyzed and calculated in the flight missions. Firstly, the simulation model of turbofan engine with ejector nozzle is established and the influence of ejector bypass ratio on thrust performance of engine is studied. Secondly, the prediction model of engine infrared radiation intensity is established based on the prediction method of infrared radiation intensity. Finally, numerical simulations were carried out for different bypass ratios and different flight missions.