Abstract: The precision evaluation of an aeromagnetic survey system is an important part of a magnetic survey. This study obtained airborne and ground magnetic data through flight experiments in a certain survey area of Inner Mongolia. Then, the high-precision ground magnetic survey data was upward-continued to the height of the flight course using the interpolation-iteration and equivalent source methods. Finally, the external coincidence precision of the aeromagnetic survey system was evaluated by comparison with the aeromagnetic survey data. The precision evaluation results of the two continuation methods are better than 5 nT, reflecting the actual precision level of the aeromagnetic survey system. Therefore, the research methods in this study can provide references for the evaluation of the external coincidence precision of an aeromagnetic survey system and can also be used for online calibration of the scale factor, deviation, and other parameters of newly developed aerial magnetometers.