In order to explore the effects of boundary inflow conditions at different time scales on the simulation accuracy of hydrodynamic water quality model of plain tidal river network, taking the middle area of Zhangjiagang, a typical plain tidal river network area, as an example, a hydrodynamic water quality model was constructed based on field synchronous monitoring data, automatic high frequency monitoring data and conventional monitoring data. The results show that the time scale, the starting time and the dispatching conditions have an impact on the simulation accuracy; the credible maximum time scale of the study area boundary inflow conditions, hydrodynamic simulation results and water quality simulation results is 1 h; and the accuracy of water quality simulation is better than that of hydrodynamic simulation.