Rocket engine exhaust plume produces a strong infrared radiation signal and is widely used for target diagnosis and detection. The traditional method for calculating the infrared radiation characteristics of the exhaust plume is difficult and time-consuming. In this paper, the engineering analytical method in the band is used to calculate the equivalent spectral radiation intensity of the exhaust plume, and the spectral radiation intensity varies with the viewing angle. The relationship curve constructs the spectral radiance intensity as a function of the viewing angle. This method does not just take advantage of the efficiency of the engineering analysis method, but also preserves the accuracy of numerical simulation. The spatial distribution of the infrared radiation intensity field in the typical band of the exhaust plume is simulated by an example. © 2020 SPIE.