Abstract: Jiaokou reservoir earthquakes in Ningbo from 2009 to 2021 were relocated using the double difference positioning method. The focal mechanism solutions of large earthquakes were calculated by HASH method. Based on the location distribution, depth distribution and overall focal mechanism solution characteristics of the earthquakes after precise positioning, the seismogenic structure and seismogenic mechanism were discussed by combining with the regional geological tectonic background, geological conditions in the reservoir area and the change of reservoir water level. The results show that the seismogenic mechanism of the Jiaokou reservoir earthquake sequence in 2009—2012 is similar to that in 2018—2021, and the regional fault Changxing—Fenghua may be the seismogenic fault. The reservoir water infiltrates through the fracture fracture zone, the pore water pressure diffuses, the reservoir water softens and weakens the rock for a long time, causing the fault plane and some weak parts in the deep part to become unstable areas, and finally triggering the earthquake under the loading and unloading stress field caused by the change of reservoir water.