Abstract: In the design of strengthening projects under dynamic compaction,the replacement depth was an important parameter.With regard to the existing problems in estimation formulas for replacement depth under dynamic compaction,a formula with high accuracy was established considering 3 factors: the compaction energy per blow,the diameter of the hammer and the soil quality.The optimum parameters were obtained by use of the nonlinear least square method.It was shown by case studies that the proposed formula was highly accurate for fitting,and it would be helpful to the design of similar projeats.