The internal aerodynamic and infrared radiation characteristics for the helicopter infrared radiation suppressor consisted of lobed nozzle and curved mixing duct were studied by numerical calculations. In the computation, the computations of 3-D flow field and wall temperature and infrared radiation are integrated with. Compared with the experimental data, it is indicated that the relative error between the computational and experimental results is about 15%. The spatial distribution of infrared radiation intensity from computation has the same law as that from experiments. And a series of computations are conducted to obtain the effect of model scale on the wall and plume radiations. The results are verified with the nature the physics process.