Abstract: The infrared radiation in 3-5 m band of axisymmetric Laval nozzle in underexpanding, designing and overexpanding conditions were simulated by a three-dimensional(3-D) exhaust system infrared radiation code. The 3-D flow field of the jet was simulated numerically by finite volume method(FVM), RNG k- turbulence model, and the infrared(IR) radiation code of the plume was developed by FVM coupled with narrow band model in non-gray absorbing-emitting media. The results indicate that the plume IR radiation intensities of underexpanding state are maximal, those of the designing and overexpanding decrease in turn, which related to flow characteristics, it illuminates that the IR radiation of plume canbe affected by the flow characteristics, that canbe controlled by controlling the flow.