To complete the gun aiming angle variation test, this paper puts forward a new high precision of gun aiming angle test method. In a 3-dimensional coordinate measuring machine, aiming angle is tested by the selection of gun barrel in a certain position as the origin of a coordinate system, and it is solved that time consuming of the traditional method using plate and adjusting the clip for gun positioning and low accuracy problem. The new method and traditional method are compared, and the test error formula is derived to find that cumulative test error of new methods is smaller in theory. The simulation model of barrel built by SolidWorks is input into ANSYS and meshed, the mean value of data in practical test as a load is applied to the simulation model and simulated, and origin point selection is made sure with gun barrel fixed in the 3d coordinate measuring machine. In the verification experiment, the actual test results data are fit and the very high consistency is found. The results show that, the new test method of gun aiming angle is simple and precise, and satisfies the requirement of gun aiming angle variation test.