The Position and Orientation System (POS) is a critical element in mobile mapping systems. Because of the complex system integration, the center of the POS is hard to observe. Thus, a cooperative target could be used for tracking the motion state of a POS, if the relative position between target and A POS is determined. Based on the positioning equation for mobile mapping systems, we analyze the calibration techniques for cooperative target lever-arm parameters. An error model was designed for predicting the accuracy of mounting parameters of cooperative targets, with consideration of the impact from errors such as laser ranging error, angular measurement error, position error, orientation error, and scale factor error. Outdoor experiments were carried out to verify the feasibility of this calibration method, verifying that it could be used for testing the dynamic position accuracy of POS.