基于矢量折射定理推导了光束经过正交双棱镜后的偏转表达式．给出了装置的主要设计参量；用数值模拟的方法分析了主要误差项，求出了总误差和实际准确度指标．结果表明，光束在水平张角及垂直张角500 μrad内可实现准确度优于0．8 μrad的偏转，偏离准确度主要受随机误差影响；反映到棱镜转角上的总误差为12．72 arcsec，引起的光束偏离误差为0．365 μrad，大于系统读数分辨率0．0387 μrad，且小于光束偏离准确度指标0．8μrad．

The deflection expressions,based on the vector refraction theorem,are derived from the light beam deflection through a pair of orthogonal prisms,and the main design parameters of the device are confirmed. The main error items are especially analyzed by the method of numerical simulation,and the total error and the actual precision index is also presented. The result shows the light beam,with the deflection precision of less than 0.8μrad,can be deflected 500μrad in both the horizontal and the vertical field angle,the deflection precision of which is mostly influenced by the random errors. The total error converted on the rotation angle of prism is 1 2.7 2 arcsec,which causes the deflection error of light beam 0.365μrad,greater than the reading resolution of system 0.0387μrad and less than the precision index of light beam deflection 0.8μrad,so the design is rational and feasible.