The invention belongs to the technical field of flood dispatching and provides a basin reservoir group and district flood combined dispatching method and system. The method comprises the steps of: defining reserved ports; establishing an instantaneous unit hydrograph equation; processing flood flow of a target basin by using a Muskingum algorithm and obtaining a flood hygrograph; according to the structures of flood discharge buildings in the target basin, acquiring a current form and a critical point; according to the current form and the corresponding critical point, acquiring a discharge quantity valve via recursive computation. The basin reservoir group and district flood combined dispatching method and system can calculate flood accurately according to the features of hydrologic basins, and thus achieve flood combined dispatching for reservoir groups and districts and simplify the complexity of calculation.