针对某多波段共口径长焦距反射式红外成像系统最小可分辨温差（minimum resolvable temperature difference，MRTD）在实验室条件下的测试结果偏离设计值这一现象，从MRTD的定义入手，详细梳理了观察频率响应、视觉角、采样相位传递函数等因素对MRTD测试结果的影响，重点分析了采样相位对红外系统静态和动态MRTD的影响情况，论证了空间频率在 $0.6\;{f_N}$～ $0.9\;{f_N}$区间内，静态MRTD测试值会偏离设计值。最后，通过实验室测试验证了采样相位传递函数是影响红外成像系统MRTD的主要因素。

Aiming at the test results of minimum resolvable temperature difference (MRTD) of a multi-band common aperture long focal length reflective infrared imaging system deviating from design value under laboratory conditions, starting with the definition of MRTD, the influences of observation frequency response, visual angle, sampling phase transfer function and other factors affecting MRTD test results were analyzed in detail. Secondly, the influence of sampling phase on infrared system static and dynamic MRTD test results was emphasized. It was demonstrated that static MRTD test value would deviate from the design value when spatial frequency was in the range of $0.6\;{f_N}$～ $0.9\;{f_N}$. Finally, combined with the test data, it was proved that sampling phase transfer function was the main factor affecting the MRTD of infrared imaging system.