To evaluate the flood risk of Black River efficiently and conveniently, the deluge gradual processing in black river gold basin reservoir is established within the one-dimension model and two-dimension model of hydrodynamic coupling. Triangular unstructured grid is adopted to accommodate height and large span, as well as complex underlying surface of Mountain Rivers. Lateral connection, time synchronization and corresponding coupling space node are applied within coupling of one-dimension model and two-dimension model. The numerical simulation of flood in Black river gold basin reservoir which is in different frequencies is in the framework of established coupling model. As a result, the water depth and distribution of flow field in different time are obtained within the calculation areas. Based on the results of coupling simulation, the flood risk map and the analysis of importance of dam break as well as the risk of flood-hit population proceeded. The results coming from the mentioned simulation could provide basis to alarm of Black River flood and evaluation of disaster loss.