无热化设计是利用不同手段消除环境温度变化对光学系统性能的影响。针对红外光学系统，提出一种光学被动式无热化设计方法。从单个透镜出发，列出透镜组的消热差方程组，通过笛卡尔坐标系描绘出常用红外材料的消热差系数和消色差系数，使用图解方法求得红外材料的合理组合，同时得到归一化的组合光焦度分配。最后用实例说明光学被动式无热化设计的求解过程，并通过光学设计软件对结果进行分析，说明该设计结果在-40℃～+60℃温度范围内均满足消热差和像差要求。

Athermalization is to eliminate the ambient temperature effect on the performance of optical systems. A passive optical athermalization design was proposed for infrared optical systems. Proceeding from single lens, a set of equations to eliminate the thermal difference of lens group was given. The coefficients for eliminating the thermal difference and chromatism of common infrared materials were described by Cartesian coordinates. The rational combination of infrared materials was derived with the graphical method, and the normalized distribution of focal power was obtained as well. The design process of the passive optical athermalisation was elaborated by an example. The result was analyzed with an optical design software. It shows that the design result meets the requirement of eliminating the thermal difference and chromatism at the temperature range of -40℃～+60℃.