Abstract: On July 12, 2020, an M_S5.1 earthquake occurred in Tangshan Guye of the Hebei province. In order to explore the abnormal information of lithospheric magnetic field before the earthquake, the data processing of mobile geomagnetic vector monitoring is processed, and the annual variation model of lithospheric magnetic field in Hebei region from April 2019 to April 2020 is obtained. It is found that the epicenter is just on the zero value line of D component of magnetic declination, and there is a certain area of significant positive anomaly area in the eastern part of the earthquake area. Two half year lithospheric magnetic field models from April to September 2019 and from September 2019 to April 2020 are added, and it is found that the positive anomaly area is reflected in the former. Therefore, we judge that the abnormal accumulation time is earlier. The geomagnetic relative records of Changli station in the east side of epicenter and Hongshan Reference Station in Southern Hebei Province from June to December 2019 are compared, it is inferred that the accumulation of positive anomalies of D component began in the last year. The occurrence of the positive anomaly area may be related to the stress concentration and abnormal accumulation caused by the transfer of the near East-west principal compressive stress to the intersection of the two groups of faults in the east of the earthquake area.