Based on theory analysis and numerical simulation method, a heating model on the irradiated structure component of optical system and an illuminance distribution model on infrared radiation from the structure and optical components on focal plane are built. On the basis, simulation software is compiled. Through the calculation results from the software, the distribution of temperature improved due to the laser irradiating the infrared optical system and the effect of second radiation of the optical and structure components are analyzed. The effect of temperature improved on an optical system with typical structure is performed simulation calculation, and the effect of second radiation to the detector is discussed. It is found that even the wavelength of incident laser is not matched to the operation wavelength of the infrared detection system, the detection efficiency can be reduced obviously by second radiation.