According to the distribution of seismic stations and the ambient noise in the Capital area，we estimated the monitoring ability of the Beijing，Tianjin and Hebei Digital Seismic Networks，and then according to the catalogue produced by the China Earthquake Networks Center，we gave the picture of the factual locations of the earthquakes. The result shows that we should build more stations in the two faults in Capital area to enhance the monitoring ability to benefit the monitoring ability and earthquake forecasting in the Capital area.