Based on a 1D finite moving source model propagating unilaterally with uniform velocity, the rupture transmission in one direction is superior to that in other directions.According to the Doppler Effect in the earthquake rupture process, the seismic wave frequency received by earthquake stations changes in different directions and thus, we can use the directional change of the corner frequency of the P or S waves to obtain the source parameters of the fault plane.In this article, the azimuth of rupture propagation direction and source parameters of the fault plane of the July 20, 2012, M_S4.9 earthquake at the boundary zone of Gaoyou and Baoying in Jiangsu Province are obtained using the directional change of the corner frequency of the P and S waves, respectively.The azimuth angle of the fault plane for this earthquake was determined to be 232° by the P waves and 233.5° by the S waves, the seismic Mach number (v/c) was about 0.18 by the P waves and 0.23 by the S waves, and the fault length was about 0.26 km by the P waves and 0.18 km by the S waves.The result inverted by the corner frequency of the P and S waves is consistent, which shows that the azimuth angle of the fault plane for this earthquake was about 232°. Because of the lack of a near-station record at an azimuth of 49°, the inversion method is based on a 1D finite moving source model propagating unilaterally with uniform velocity.Therefore, the result of a rupture azimuth of 232° cannot represent a rupture propagating in the direction from NE to SW;it only indicates that the rupture surfaces were aligned in that direction.The seismic Mach number was about 0.2, which shows that the rupture velocity was smaller than the S wave velocity, and the fault length was about 0.2~0.3 km. Many scholars have studied the seismogenic structure of the earthquake on July 20, 2012, using a variety of methods such as focal mechanism solutions, field seismic intensity investigations, and relocation for aftershocks;however, the results have not been the same.The results of focal mechanism solutions show that the strike angle of one fault plane is 14°~28° in the NNE direction, whereas the strike angle of the other is in the NWW direction.Analysis shows that the fault plane might be in the NNE direction;however, the results of both field seismic intensity investigations and relocation for aftershocks show the fault plane might be in the NE direction.Our result show that the fault plane is aligned NE-SW, which is in accordance with the field seismic intensity investigations and relocation for aftershocks.The result inverted by the corner frequency of the P and S waves is consistent, showing a rupture azimuth with NE-SW alignment, which indicates that this method is meaningful in the fitting of the azimuth angle of an earthquake fault plane.Combined with regional geological structural data, we suggest that the Chuhe fault is likely to be the seismogenic structure of the M_S4.9 earthquake at the boundary zone of Gaoyou and Baoying.