Abstract: Three-dimensional numerical simulation was carried out to investigate the internal aerodynamic characteristics insides the single-stage ejection and multi-nozzles infrared radiation suppressor used in the helicopter. Conclusions can be drawn as follows according to the simulation conditions:(1)This kind of infrared radiation suppressor has an impressive ability to pump secondary flow,the pumping ratios for three individual mixing duct differ obviously and the total pressure recovery coefficients are almost the same. (2)The primary flow velocities and pressures at multi-nozzles exit are the same,the important factor affecting the pumping ratio of the individual mixing duct is the secondary flow's smooth level.(3)The decay of the primary flow core velocity and temperature is relative to pumping ratio for three individual mixing ducts.