简述了空间激光通信中精跟踪系统的组成和控制结构，分析了捕获、跟踪、瞄准系统精跟踪探测器使用质心算法进行信标光斑定位时的误差来源，对精跟踪探测器信标光斑定位过程进行傅里叶频域分析.推导得到消除质心算法系统误差的理论方案，即信标光波长和精跟踪系统的F数乘积需大于精跟踪探测器的像元尺寸.分析了精跟踪系统实现过程中关键参数的选取过程，结合精跟踪系统的系统参数耦合关系，为了不损失精跟踪视场，在精跟踪探测器镜头前添加孔径光阑进行精跟踪系统优化，以消除精跟踪探测器光斑定位时的系统误差.理论计算和实验证明：当孔径光阑的直径小于9.32 mm时，精跟踪系统的相对孔径小于0.045，精跟踪误差仅为0.03 pixel，相比优化前的精跟踪系统，跟踪精度提高了1.9倍.

The composition and control structure of fine tracking system of free space laser communication are briefly described. The error sources of the beacon positioning of fine tracking detector using centroid algorithm of the acquisition, tracking and pointing system are analyzed. And the Fourier frequency domain of the beacon positioning process of fine tracking detector is analyzed too. The theoretical scheme for eliminating the systematic error of centroid algorithm is derived, that is, the product of the beacon light wavelength and the F number of the fine tracking system need to be larger than the pixel size of the fine tracking detector. The selection process of the key parameters in the implementation of the fine tracking system is analyzed，and considering the coupling relation of system parameters of fine tracking system, in order not to lose fine tracking field of view, the optimization of fine tracking system by adding aperture diaphragm before fine tracking detector lens is implemented for eliminating the systematic error of centroid algorithm. The theoretical calculation and experimental results show that when the aperture diameter is less than 9.32 mm, the relative aperture of the fine tracking system is less than 0.045, and the fine tracking error is only 0.03 pixel, and the tracking accuracy is improved by 1.9 times.