Abstract: The geomagnetic observation data of FHD-2B at Datong seismic station in Shanxi is mainly affected by the interference of the instrument’s own observation system and the surrounding environment. Since the performance of the instrument is nearly stable after delivery, we can improve the quality of observation data by improving the environment. In this paper, the quality of observation data from 2017 to 2021 was evaluated from three aspects: continuity rate, integrity rate and background noise, and it is found that the background noise level of the instrument has been significantly reduced since the instrument was updated in June 2019. By analyzing the data curves of different interferences such as construction interference, vehicle interference, high-voltage direct current transmission interference and power failure, it is found that the construction interference is generally manifested in the same period of time when each component is interfered, and the interference amplitude is different; the interference of high-voltage direct current transmission is usually serious in Z component, which can be processed through the interference period given by the National Geomagnetic Network Center and combined with the data of surrounding geomagnetic stations; vehicle interference interferes with each component of data, corresponding to vehicle activity period; the power failure interference shows that the observed data curves of D, H and Z components become thicker, burrs increase, and even wrong data appear, which can be solved by modifying the parameters of the instrument home page. The characteristics of different interference curves are summarized, which is convenient for workers to use FHD-2B geomagnetic data correctly for seismic research.