Abstract: Based on investigation of the distributing and distortion break characters of ground and building fissures at the city zone of Yajiang county, its growth rule was summarized, and its forming mechanism was analysed combining geological conditions such as slope geological structure and groundwater. Its forming mechanism is that the relax soil lies on the front and back zone of slope which structure is complex creeps and glides bringing on asymmetry subsiding. Besides, earthquake accelerates its form and expanding. The research production is important signification for integer stability appraisement of the city zone slope, the town planning constructing and making choice of normal sluice place Yagen hydroelectric station downstream of Yalong river. Furthermore,it is certain meaning for cognition to the causation of building crack at the county in a mountainous area.