Abstract: The focal depth of Gaoyou M4.9 earthquake on July 20, 2012 is analyzed using the PTD method and two key issues about the seismogenic structure of the earthquake:whether Chuhe fault extends to the epicenter, whether Linze fault has an deep structural condition for moderate-strong earthquake is discussed combining with previous research results of regional deep structure, tectonic deformation, geophysical profile feature, statistical results of focal depth etc. The results show that as an important controlling fault during Indosinian-early Yanshan epoch in the foreland basin, the Chuhe fault pass through Tianchang and the part of which in North Jiangsu is made up of three faults, the Yangcun fault, the Shigang fault and the Jianhu fault, it extends northwest and not to the epicenter. The Linze fault is a normal fault of Cenozoic era which is reversed from a Mesozoic thrust fault, as a boundary fault of Liubao low uplift and Linze sag, its decoupling depth in the deep crust is close to the focal depth of the earthquake sequence, its geometric features and tectonics is consistent with the aftershocks distributions, seismic intensity, focal depth and the focal mechanism solution. Comprehensive analysis indicates that the Linze fault may be the seismogenic structure of the earthquake.