目前已有多种红外系统作用距离的方程，但都有其各自的适用性和局限性。通过对已有的基于对比度的作用距离方程进行分析，发现其没有考虑成像弥散和路径辐射的影响，并且只能针对单一波长的目标。综合考虑成像弥散和路径辐射对红外系统作用距离的影响，对原有基于对比度的作用距离方程进行了修正，得到基于对比度的红外系统对点源目标的作用距离方程。该方法的预测结果和外场的实验数据比较，具有较好的一致性，证明了该方法的有效性。

Currently there are a variety of functions for operating range calculation of infrared systems, each has its own applicability and limitations. Analysis was made to the existing operating range function based on contrast ratio, which showed that the effect of diffusion imaging and path radiation were not taken into consideration in the function, and it can only be applied to the target with a single wavelength. In this paper, the impact of diffusion imaging and the path radiation on the operating range of infrared systems were taken into consideration, the operating function based on contrast was modified, and a contrast-based function of infrared system's operating range to point targets was obtained. The forecasting result of this method was consistent well with the actual experimental result, which proved the validity of the method.