Abstract: In this paper, we calculate the differences of a geomagnetic field between observatories and the main magnetic field by using NGDC-720 model and observed data collected at 36 stations from 2008 to 2015 in the Chinese mainland area. The accuracy and applicability of the IGRF12 and WMM2015 models were evaluated with the RMSE. The results suggest that:the IGRF12 model is in good agreement with the annual mean value of geomagnetic observatories; but for different stations, the precision of IGRF12 model presents a huge difference. The model error in IGRF12 and WMM2015 have similar spatial distribution characteristics, and the maximum, minimum, and as root mean of magnetic elements are very close to one another. The RMSE of declination and the total magnetic field were 16'and 124.96 nT. Therefore, in studies of regional geomagnetic anomalies, regardless of the IGRF12 or WMM2015 as main magnetic field, both are feasible.