Abstract: To analyze the arching effect of moraines when tunnels pass through moraine layers, this study investigated the characteristics of moraines in various regions and derived the equation for the equilibrium stress arch axis of the moraine surrounding rock based on the Protodyakonor′s theory. Then, using a developed arching effect sleeve test apparatus, the arching height of the moraine was measured under different particle gradations and moisture contents to analyze their influence on arching characteristics. The study results indicate: (1) The equation for the equilibrium stress arch axis of the moraine surrounding rock is a quadratic function; (2) The mass of debris and the arching height are inversely proportional to particle size. During the free fall of granular material, the ultimate shape of frictional dilatancy self-stabilization is conical; (3) The greater the non-uniformity of the particle gradation and the smaller the particle size, the higher and less stable the arching height; (4) Under different gradations, the heightspan ratio decreases with the increase of relative particle size, but decreases with the increase in fine particles smaller than 2 mm; (5) Within a certain range, as moisture content increases, the height-span ratio gradually decreases,and the rate of decrease becomes smaller.