Based on the numerical calculation of three-dimension flow field of the exhaust system, a code is developed by the reverse Monte-Carlo method (RMCM) to simulate the infrared radiation characteristics of the aeroengine exhaust system and the plume. A ray-tracing method (RTM) is introduced to seek the meshes of the flow field which the ray travels through to avoid the trouble of interpolation. The infrared radiation characteristics of a certain turbo-fan engine’s ejector nozzle in the waveband of 3-5μm is simulated at non-afterburning condition. The results of the simulation show that : (1)Because of the introduction of the secondary flow, the average temperature of the ejector nozzle’s core plume is 20K lower than the baseline one’s.(2) The infrared intensity for the ejector nozzle is most reduced relatively by 44.5% in comparison with the baseline nozzle along lateral direction.(3) The ejector nozzle has a better performance of infrared stealth.