利用光学不变量对焦平面系统进行近轴分析，得到了量化焦平面系统冷反射集中程度和变化率的两个一阶参量。以热辐射理论为基础，推导并总结了冷反射引入温差（NITD）和成像系统参数及环境参数的关系式。以焦距为90 mm，视场角4°，F数2.75的中波焦平面成像系统为例，在CODE V软件中对其冷反射效应进行了定量分析，并以一阶参量为约束，实光线追迹辅助验证的方式进行了冷反射优化,优化后光学系统的冷反射降低了70%。在杂光分析软件(ASAP)中根据系统的实际参数对冷反射分布进行了模拟，结果表明对冷反射进行优化控制后，系统的NITD减小到了预设值之下，冷反射效应得到了很好的控制。

Cooling IR focal plane system is paraxially analysed with the optical invariant and first order parameters are proposed which quantify the concentrition and variation of narcissus on focal plane arrays (FPA). The ralation between NITD and parameters of environment and system is summarized based on the theory of thermal-radiation theory. The narcissus of an optical design in 3~5 μm with F-number 2.75, view angle 4° and effective focal length 90 mm is caculated and optimised through controlling its first parameters and using real ray trace as confirmation in CODE V, after which the narcissus effect drops by 70%. The distribution of narcissus is simulated on practical conditions in ASAP and the results are presented, it is shown that the NITD dropped down below the preset value after optimization and the narcissus is controlled effectively.