Aiming at the current error problems in the calibration of the optical axis of the high-precision optical system， a method based on the equivalent nodal point theory to calibrate the actual optical axis of the system is proposed. By establishing reference coordinate system， the nodal point coordinate systems and the detector coordinate systems， and combining with homgenours coordinate transformation method， a mathematical model suitable for the optical axis calibration of an actual system is established. The optical system with a 100 mm focal length and a 20 mm distance of optical nodal points is taken as an example to analyze the factors that affect the calibration accuracy， and the result show that the calibration calculation error introduced by collimators， rotary table， and calibration model is less than 10''. It provides a method and reference for the accuracy analysis of optical axis calibration for different optical systems based on the equivalent nodal point theory.