In this paper, the bad condition of back mathematical calculation procedure of Muskingum method has been analyzed in terms of theory, by applying 8 spline function to repair hydrograph and employing straight calculation for the condition of x being small, the continuous operation of back mathematical calculation procedure of Muskingum method for several river stretches can be calculated and the satisfactory results have been obtained. Thus, this mathematical calculation method is practical in engineering hydrology designing.