Abstract: This paper analyzes the characteristics of the external interference field and the near-field of a satellite to see how the precision is affected by the outer interference magnetic field in the magnetic tests under geomagnetic environment. By properly placing the sensors monitoring the outer interference magnetic fields, arranging the satellite's magnetic sensors, with the help of signal processing functions for the dynamic magnetic fields such as A/D sampling scan frequency cycle control, the signal statistics, the filtering waves, and the data fitting, we have achieved the synchronization, the equivalencies, the consistency of the interference signals between the monitoring sensors and the collection sensors, and the non-interference between the real and the interference magnetic fields in signal collection, the effectiveness of the closed-loop control, the auto-detection, and the compensation and the revision of the outer interference magnetic fields under dynamic magnetic environment. The outer interference effects are avoided in the magnetic tests. In the real-time monitoring under the harsh environment, the magnetic interference fluctuations are kept within the range of 0.5-1 nT. The test environment conditions of 24h quasi-zero magnetic field are achieved with satisfaction of the technical requirements of the magnetic environment for the magnetic tests of satellites.