In this paper,we relocated 6,463 small earthquakes which occurred from October 2008 to March 2020 in Beijing area(39.2°N～41.2°N,115.2°E～117.6°E). We obtained the spatial distribution of 4,776 relatively high precision seismic events by using the double-difference relocation algorithm. The results show that the root mean square (RMS) of travel time residuals significantly decreased,the relative position accuracy between seismic events are significantly improved,and the clustering of seismicity is closely related to active faults. Based on the results of relocation,we discussed the relationship between the activity of small earthquakes and deep and shallow structures of active faults,and came to the conclusion,in which the Xiadian fault is of strong small earthquake activity with the epicenter distribution closely to the fault in space,resulting in a NE trending linear distribution along the fault strike. Combined with the results of artificial profile detection,we speculated that the wide cluster area near the 10km depth of the small earthquake concentration zone in this area is mainly caused by the shallow listric faults activity,and the relatively narrow near vertical small earthquake cluster near 14～22km is caused by the activity of deep fault. The fault in the north margin of Huaizhuo subbasin is active in small earthquakes. The depth profile of small earthquakes in this area reveals that the fault is a listric fault inclined to southeast,steep in the upper part and gentle in the lower part. Combined with the analysis of the results of artificial profile detection,it is considered that the coexistence of deep and shallow faults and the inhomogeneous crustal structure are tectonic background of moderate strong earthquakes. There exists a strong correlation between the distribution of small earthquakes in the plain area and the distribution of Quaternary faulted basins. The Changping-Haidian small earthquake concentration area,Shunyi small earthquake concentration area,Xiadian small earthquake cluster area and Langfang small earthquake cluster area are respectively located in Machikou-Shahe fault basin,Shunyi fault basin,Dachang fault basin and Gu'an-Langfang-Yongqing fault basin. According to the spatial distribution characteristics of small earthquakes,it is inferred that there is a buried fault under the small earthquake concentration area in the southern mountainous area of Huairou,and there is a NW or NWW trending buried fault under the NW trending small earthquake concentrated distribution area between Baodi and Xiadian Fault.