Polarizing beam splitter cube (PBSC) is the core of the polarization measurement system. The machining and assembly error of the optics component directly affects the polarimetric detection deviation. By analyzing the interaction between the incident light and the optics component, the ratio of the partially polarizing beam splitter cube is deduced, and the result theoretically shows that the best ratio is 78.9/21.1. The detection deviation of PBSC is presented with the change of the incident light polarization angle. The effect of half-wave plate (HWP) and quarter-wave plate (QWP) assembly angle deviation is included when splitting ratio deviation is ±2%. It theoretically indicates that to meet the polarization detection deviation less than 2%, the ratio deviation of PBSC should be less than ±0.5% and the HWP assembly angle deviation within ±0.5°. The effect of QWP on the detection deviation can be strongly ignored when the assembly angle deviation is within ±2°.