泛卡塞格林光学系统结构简单、像质优良，广泛应用于空间光学领域中。从对研制完成的谱段位于500～800 nm的泛卡塞格林光学镜头的调制传递函数（MTF）的测量结果出发，结合泛卡塞格林光学系统的结构特点，分析表明光学设计的色差来源于其高次施密特非球面镜，提出了一种利用非球面镜的最小色差条件来改进光学系统的新方法。通过三级像差理论，分析了施密特非球面镜的面形方程，计算出最小色差条件及相应的中性带高度，进行光学设计的优化改进，取得了良好的效果。结果表明，改进后光学系统的色差由原来的31.4 μm减少为4.25 μm，且光学系统的MTF值达到0.6以上（40 lp/mm），像质优良。该方法为类似光学系统的设计提供了一定的参考价值。

With the advantage of its simple structure and good image quality, the pan-Cassegrain is widely used in the field of space optics. Based on the modulation transfer function (MTF) measurement results of the pan-Cassegrain optical lens with the spectrum band of 500~800 nm, and combined with the characteristics of pan-Cassegrain optical system, the cause of chromatic aberration is analyzed, resulting from its high-order aspheric, and a new method to improve the perfermance the optical system is proposed correspondingly based on the minimal chromatic aberration of aspheric. According to the third class optical aberration theory, the surface equation of Schmidt aspheric is analyzed and the minimal chromatic aberration and its zone-aperture height are figured out. Improvement of optical system is achieved correspondingly and the results show that the full-aperture spherochromatic aberration of improved optical system is reduced from 31.4 μm to 4.25 μm, and its MTF values are more than 0.6. The results provide a good guiding to the design of other similarity optical systems.