系统的作用距离是评价系统性能的主要指标，它除了与系统参数有关外，还与目标、背景等相关联。背景环境的辐射分布，引起距离计算结果的起伏。本文提出了距离的概率分布函数作为系统的性能指标，提高了系统评价的准确性。文中结合亚毫米波段在Ｐｌａｎｃｋ与ＲａｙｌｅｉｇｈＪｅａｎｓ公式之间存在着转换波长，分别给出了近亚毫米与其它波段中使用的公式，为进一步研究提供依据，并且这种方法可推广到多个独立参量分布的处理中，但数学描述的复杂性增加 The system of distance is to evaluate the performance of the main indicators of the system, which in addition to the system parameters, but also with the target, background and so on. Radiation distribution of the background environment, causing fluctuations in the distance calculation results. In this paper, the probability distribution function of distance is proposed as the performance index of the system, which improves the accuracy of the system evaluation. In this paper, we present the conversion wavelength between the Planck and RayleighJeans formula in the sub-millimeter waveband, and give the formulas used in sub-millimeter and other waveband respectively, which provide the basis for further research. And this method can be extended to many independent The distribution of parameters is processed, but the complexity of mathematical description increases