To improve the accuracy of spacecraft attitude determination, a high-precision calibration method for star sensor optical axis is proposed. Firstly, the star sensor optical axis error model is established. Then, the observation equation is established based on the reference vector and vectors measured by star sensor optical axis. The error angle is estimated based on the Kalman filter, and finally the mounting installation error of the star sensor is corrected. The results of mathematical simulations demonstrate that presented approach markedly enhances the spacecraft attitude determination precision.