Abstract: The concept of "equivalent quasi-static force" between the tamper and the ground was proposed for the analysis of dynamic compaction,and the basic expression to compute the "equivalent quasi-static force" was deduced from the work-energy principle.By introducing the 1D stress-strain relation of cohesionless soil and the stress distribution,together with the empirical relations between the designations of in-situ tests and the engineering properties of granular soils,a simplified approach(quasi-static analysis) and the values of related parameters in this model were proposed for the evaluation of the improvement effect of dynamic compaction for granular soils,which could predict the crater depth,the relative density and SPT blows at different depths under the tamping points in the process of tamping.It was indicated by case studies that the proposed method and values of parameters,regardless of its high simplification,were practically feasible.