To improve the stray light testing ability and calibration accuracy of the stray light equipment used in test of the Point Source Transmittance (PST), a calibration lens was proposed to calibrate the testing range and testing accuracy of the equipment in a large off-axial angle. By using a simple physical model, the calibration lens was designed in a laboratory. The physical parameters of the calibration lens were measured, then these parameters were taken into the TracePro to calculate the PSTs in different off-axial angles. Finally, the calculated result and the tested result of PSTs were compared, and the test accuracy of the equipment were obtained. The experimental results indicate that the difference between calculate results and testing results of the calibration lens is better than lg/0.5, meeting the need of testing accuracy calibration of the stray light equipment in testing PSTs and providing a reliable reference for the absolute measurement of PSTs. This technology solves the problem in testing accuracy calibration of PST measuring systems.