Based on the measuring benchmark of higher precision, the inner orientation elements of star tracker were modeled and optimized. Because of the fact that the error of the optical system with large FOV is not ideally axial symmetry, a calibration model based on net zone-division field of view and the corresponding optimization method was proposed to calculate inner orientation elements of star tracker. Firstly, the principle point and focal length were resolved based on pinhole model after the compensation of initial alignment error. Then, the polynomial combined with bilinear interpolation was used to correct the optical distortion under the guidance of zone-division modeling theory. Finally, measurement angle error was applied to the accuracy evaluation of calibration. A calibration experiment in lab and a real sky test validated the proposed method with the residual error of x axis decreased by 35% and y axis decreased by 20%.