Abstract: Forecast of dam-break flood discharge of barrier dams is extremely important in its emergency rescue process. Based on the measured flood discharge at the downstream hydrological gauge stations of the Baige barrier dam on the Jinsha River, we perform back analysis on the natural overtopping discharge process, using DB-IWHR dam flood analysis program and GST flood evolution model. The results show that when erosion parameters a, b was respectively 1.1000 and 0.0006, the inversion results best fit the measured discharges. It was concluded that the dam breach has a peak flow of 10882.78 m3/s occurring at 6.2 h after the breach, and the final breach width was calculated to be 99.66 m. This work also demonstrated the efficiency of DB-IWHR and GST in flood evolution calculation in emergency rescue works.