A system modeling method based on solar vector is proposed to improve the system modeling and pointing accuracy of convex mirrors which are used as reflective light sources. The fitting coefficient (R²) of 0.999 or higher obtained by linearity fitting of experimental data ensures the reliability of our experimental data. The model is solved by the least-squares method,and inherent geometric errors of the system are obtained. Finally, the correctness of the calibrated model is verified by using the reverse model to solve the target value and comparing the centroid of the sun image. The experimental results show that the angle of the target encoder is essentially the same as that of the actual measurement. To summarize, the standard deviation of pitch angle error is 0.0043°, standard deviation of azimuth angle error is 0.00299°, error range is kept within 0.04°, difference of image centroid pixel is approximately 2 pixel, angular resolution error of pixel is approximately 0.036°, and comprehensive pointing accuracy of the system is better than 0.1°. Therefore, the validity and feasibility of this method are verified; this lays the foundation for the on-orbit absolute radiometric calibration of multi-spatial resolution optical remote-sensing satellite sensors with high accuracy, high frequency, and operational and full dynamic range.