This study takes Moyang River basin, which is lack of hydrologic data, as the research object to simulate the temporal and spatial distribution of water flow through HSPF (hydrological simulation program-Fortran) model, and calculates the temporal and spatial distribution of chemical oxygen demand (COD) and ammonia nitrogen water environmental capacity using one-dimensional steady-state water quality mathematical model. Results show that 1) HSPF model’s yearly and monthly hydrological errors are below 15%, Nash-Sutcliffe coefficient is over 0.9; the relative error of the water quality model is around 10%, Nash-Sutcliffe coefficient over 0.8. 2) Under 90%, 50% and 10% assurance rate, COD capacity of Moyang River basin is 164500 t, 218400 t and 249700 t respectively, and ammonia nitrogen is 5100 t, 8800 t and 11400 t respectively. Affected by seasonal runoff fluctuations, difference of water environment capacity between dry season and wet season is obvious. The variation of water environment capacity in January is minimum and June the maximum. 3) Bearing capacity of main stream of Moyang River is larger than that of the primary and secondary tributaries. Therefore, in some basins where hydrological data is lack, HSPF model can be applied to simulate the hydrology, analysis time and space distribution of water environmental capacity, and provide guidance for the establishment of total amount control scheme of water environmental capacity.