In numerical simulations of debris flow and evaluations of sabo dam mitigation effects, one of the most important issues is the estimation of overflow discharge across a sabo dam. In this study, under the assumption that complete overflow and free overfall equations are applicable to a one-dimensional (1D) simulation of debris flow, the coefficients of these equations are derived from a regression analysis of experimental results and validated by comparing them with experimental results with two sabo dams. The proposed coefficients for both the equations are related to sediment concentration, which reproduced the time change of flow discharge and sediment concentration overflowing the sabo dam better compared to the conventional values of those coefficients.