Abstract: In the mobile geomagnetic vector measurement, it is necessary to know the accurate geographical azimuth first, and then the magnetic declination can be obtained. In the field survey, the GPS static observation orientation method is used to obtain the geographic azimuth. Based on the existing baseline observation and calculation methods of the mobile geomagnetic monitoring team, this paper provides an accuracy estimation model by evaluating the accuracy of the actual observation data, and finds out the main influencing factors that affect the accuracy of GPS short baseline orientation. The results show that in geomagnetic vector measurement, the main sources of error in baseline orientation are antenna phase center deviation, multipath effects, and receiver noise; the ratio between northward accuracy and eastward accuracy is about 1∶2, and height direction accuracy is the lowest; orientation accuracy is not simply inversely proportional to distance. As a result, some measures are put forward, such as controlling monitoring point selection, improving the antenna of GPS receiver and calibrating the GPS antenna to improve the GPS short baseline orientation accuracy.