Abstract: The deficit in soil moisture or soil moisture storage capacity for a particular point is estimated based on the van Genuchten soil water characteristic curve model. The deficit is then used together with the relationship between the depth to groundwater table and the TOPMODEL topographic index in the development of a watershed storage capacity model taking into account the effect of soil properties and topography. Based on statistical analysis of the storage capacity of each grid point, the watershed storage capacity curve can be obtained. The watershed-scale capacity curve is used to replace the calibrated storage capacity curve of the traditional Xin'anjiang model. The Ziluosha sub-basin of Huaihe River basin is chosen as a test site to validate the new model and to study the influence of terrain and soil types on the watershed storage capacity. Results show that the new model can better simulate the event-based flood hydrograph compared to that obtained with the traditional Xin'anjiang model. The use of an explicit formula for the storage capacity in the new model reduces the number of user calibrated parameters in the traditional Xin'anjiang model, which provides a new tool for hydrological simulation in ungauged basins.