Abstract: In order to investigate the characteristics of the temporal and spatial changes of the b-value before the Tangshan M_S5.1 earthquake in 2020, this paper conducts a spatio-temporal scanning calculation of the b-value changes in the capital circle from January 2009 to before the earthquake. The results show that the b-value of the epicenter of the Tangshan M_S5.1 earthquake is well represented by the small scale area, while the b-value of the large scale area shows no obvious anomaly. At present, the Shangyi-Huai'an section of Hebei, Beijing, Bohai and other areas are in low b-value areas, and there is a possibility of medium-strong earthquakes in the future. Therefore, the appropriate research scope should be selected during the b-value study to prevent the over-large B-value abnormal area from being omitted