The attitude measurement data of remote sensing microsatellite platform has a large error with the actual attitude of imaging load. It is faced with great challenges in obtaining higher image quality and high-precision quantitative application. In order to realize the self-calibration of optical load， the constant star point is observed by optical load on orbit small hole imaging. The constant star point is observed by star sensor and optical load in orbit respectively to realize mutual calibration of optical load and star sensor. The installation error of star sensor and optical load can be corrected. Ground and in orbit verification show that， the self-calibration error of typical remote sensing satellite is better than 0.2″， and the cross calibration error of optical load and star sensor is better than 2″. Self-calibration and mutual calibration can effectively improve the in orbit calibration accuracy of optical load.