Abstract: An actual measurement model of star sensor is established by geometrical method. The effect of relative factors to the actual imaging location of navigation star is considered into the ideal measurement model of star sensor. These factors include focal length deviation, optical lens distortion, image sensor tilt, image sensor rotate, primary point bias, etc. The affecting law of the factors on angle-measuring accuracy of star sensor is analyzed. The star sensor is calibrated through the measured calibration data and the model parameters solved by least square method. The experimental results show that the angle measurement accuracy of x and y directions is 1.6″ and 2.3″ after calibration, but 19.6″ and 17.8″ before calibration.