Abstract: The anti xi-type seismic zones can be found along the Xianshuihe fault as the form of ground fractures,most of them in the form of alternative tensile-shear cracks with the compressional drumlins or the thrust. And the drumlins may usually appear in the gaps where the cracks run en echelion.On the basis of the field observations of the Daofu (M= 6.9) earthquake of 1981 and the information of the Luhuo (M= 7.9) earthquake of 1973,this paper discussed the mechanism of formation of the ground crack zones in terms of photoelastic experiment on clay.The author inclined to consider the studied ground crack zones to be the result of strik-slip movement along the Xianshuihe fault and the drumlins in the gaps between en echelon cracks were generated due to resulting adjustment in the normal direction at both terminals of the cracks from their lateral displacement. According to the shape of the drumlins and thrusting direction the author came to a preliminary conclusion that this kind of ground crack zones can be accounted for by the SSE-trending movement of the Sichuan Yunnan rhombic fault block.