When ship-borne wireless measuring devices are measuring and calibrating, they have 20" to 30" error value between the angle values got by measuring devices and that got by the earth measuring. According to tests, the problem is mainly caused by the error of axis angle encoder. So, new requirements were made for detection method of the axial angle encoder, detection density and scope increased, and correction formula of the encoder error was fit. After the test checking, the effect is better than the previous methods, the total accuracy of the measuring equipment has been improved by about 15".