Star sensor is a high precision attitude measurement instrument widely used in spacecraft. The star sensor’ calibration is very essential for the high precision measurement of star sensor. In order to improve the overall accuracy of the star sensor, a simulation analysis is carried out for the traditional star sensor calibration method. The model parameters are difficult to decouple for the traditional star sensor calibration. To solve this issue, a direct mapping calibration method is proposed in which the focal length, imaging plane tilt and distortion, etc. as a whole parameter are calibrated. This simple method can achieve higher accuracy, which avoids the shortcomings caused by the error analysis of the traditional method. Experimental results show that the calibration method fully meets the system requirements of 2″.