The GridXin’anjiang model (GXM) is used to improve the flood forecasting accuracy for small and mediumsized rivers. The effects of the flow reallocation process, storage and discharge of small reservoirs and ponds, and channel features on the runoff generation and concentration are considered in this study. With the quantitative simulation methods, the spatial distribution of model parameters is estimated based on the quantitative relationship between model parameters and underlying surface characteristics. The GXM is applied to the Hengjiang River located in Anhui Province for verifying its finescale forecasting capability. The results indicate that the model can satisfactorily forecast not only the streamflow at the outlet, but also the flood process at any interior grid cells without model recalibration. Besides, the spatiotemporal distribution of different hydrological elements, including the discharge, soil moisture and flow velocity, can be obtained from the GXM. GXM can provide abundant forecasting products for flood control of small and mediumsized rivers.