The NAM hydrological model was used to simulate the flood processes at the Xinning Hydrological Station, Zishui River. The results show that the NAM model could obtain higher accuracy. The effect of the parameters of the NAM hydrological model on the depth of runoff volume, flood peak discharge and flood peak appearance time was researched by GRA(grey relation analysis). The result obtained from an illustration indicates as follows: The influence of a shallow storage capacity on the simulated runoff depth by NAM model is greater, and that of the influx time constant for surface runoff and flow in soil on simulated runoff depth by NAM Model less. The effect of surface runoff coefficient and the influx time constant for surface runoff and flow in soil on simulated peak flood discharge by NAM model is larger, and that of the outflow time on simulated peak flow minor. The impact of the influx time constant for surface runoff and flow in soil on simulated peak appearance time is greater.