Abstract: Based on the soil mechanic model in saturated porous media,by combining viscous-spring artificial boundary with the 2-D explicit finite element method,an explicit numerical wave method is proposed to analyze the effect of the local terrain on the dynamic response of saturated site under diffracting earthquake wave field.Then,a 2-D semicircular valley model is used to analyze the topographical effect on the diffracting earthquake wave field in the saturated site.A comparison is made between the numerical solution and the far boundary solution.And the result indicates that the proposed method is correct and applicable.