从自由空间相干激光通信接收机的核心部件空间光混频器的光学原理出发，基于其在相干接收系统中所起的作用，建立了一套利用介质膜偏振分光棱镜(PBS)交叉分光构成方式的结构模型。研究结构模型中各光学元件对信号光与本振光作用的数学关系式，最终建立出空间光混频器的数学模型。该数学模型向具体结构演化，通过实验佐证了空间光混频器数学模型的正确性及其合理性。空间光混频器数学模型具体指出了各种光学元件相对摆放位置及其相对角度和相位补偿晶体的补偿范围及其调整方式，对未来高性能空间光混频的研制与改进有重大的指导意义。

From the optical principle of spatial light mixer which is the core-block of the free space coherent laser communication receiver, based on it′s importance in the coherent receiver system, a structure model of the spatial light mixer is established by dielectric film polarization beam splitting (PBS) cross-spectral. Meanwhile, the mathematical relationship of optical signal and local oscillator laser effected by each optical component in the structure model is studied and the spatial light mixer mathematical model is established finally. With the mathematical model evoluted to the specific structure, the correctness and rationality of mathematical model of the spatial light mixer are evidenced by experiment. The mathematical model of spatial light mixer points out not only the relative placement of various optical components, their relative angles, but also the compensating scope of crystal phase compensation and its adjustment method, which has a great guiding significance for the development and improvement of high-performance spatial light mixer in the future.