An autonomous star tracker is an opto-electronic instrument used to provide the absolute three-axis attitude of a spacecraft utilizing star observations. The precise calibration of the measurement model is crucial, as the performance of the star tracker is highly dependent on the star camera parameters. We focus on proposing a simple and available calibration approach for a star tracker with wide field of view. The star tracker measurement model is described, and a novel approach for laboratory calibration is put forward. This approach is based on a collimator, a two-dimensional adjustable plane mirror, and other ordinary instruments. The calibration procedure consists of two steps: (1) the principal point is estimated using autocollimation adjustment; and (2) the other camera parameters, mainly the principal distance and distortions, are estimated via least-squares iteration, taking into account the extrinsic parameters. To validate this proposed calibration method, simulations with synthetic data are used to quantify its performance considering the errors of the distortion model and calibration data. The theoretical analysis and simulation results indicate that the uncertainties of the measured star direction vectors are less than after calibration, and this can be further improved.