In this paper,a displacement error detection scheme is proposed in view of the inability to detect the displacement error between the optical axis and the mechanical axis of the Pechan Prism in a parallel optical path.A consistency detection system for the optical axis of the Pechan Prism is designed,including the detection optical path and the control optical path.The total length of these two optical paths is equal,and the MTF is close to the diffraction limit.Then,a detection optical path is built based on the designed detection system and the Pechan Prism is mounted with a diameter of 25mm.The angle error and displacement error between the prism optical axis and the mechanical axis are detected and adjusted in both the traditional parallel optical path and the detection optical path designed in this paper.Finally,the consistency accuracy of the output optical axis and the incident optical axis of the Pechan Prism is measured to be ±48″.The mounted Pechan Prism and rotating axis system are installed and adjusted in the formal system,and the consistency accuracy of the optical axis is measured to be ± 0.8 pixels,reaching pixel level accuracy.The detection method proposed in this article improves the efficiency and accuracy of installing and adjusting the optical axis of the Pechan Prism in the system.