Abstract: In the azimuth aiming system, the sensitive-axis direction of inertial unit is monitored usually with the help of right-angled prism. The azimuth aiming error was produced by the right-angled prism tilting, through building the mathematical model of the influence of prism tilting on the aiming accuracy, the accurate vector expression was founded, in addition, the conventional measuring way and technique were introduced, furthermore, a new detecting and calibrating method of prism tilting based on the rhombic prism was studied, and some leading causes that affecting the measuring accuracy of the system were discussed. Then, experiment platform was built based on our own rhombic-equipment. The acquired data proves that the measurement results are greatly influenced by the device level state along the direction of prism titling, the calibrated system has achieved high measuring accuracy less than 10. At the same time, this new system has obvious advantages on high measuring efficiency, and can be operated very simply and conveniently, it has a very important practical significance to improve the azimuth aiming precision.