Having consulted data of the two-dimensional velocity profile, the authors calculated the density layering structure along the Haicheng-Aohanqi-Bayanc-hagan section by using gravity model of variable density combinational body and automatic fitting method. According to an ’analysis of the lithologic variation characteristics of the crust and the mantle, it is held that the crust is basically characterized by the three-layer structure and that these layers are lithologically mixed with each other and show progressive and transitional relationship without distinct lithologic boundaries. The Moho in this region shows no obvious undulation which hence is not the main cause for variation in gravity anomalies. It is mainly the inhornoganeous distribution of the crus-tal and mantle materials and the layered structure that determine the shapes of gravity anomalies. The results of this research provide new basis for prognosis of geological structures and ore resources in this region.