Obtaining the spatial distribution of free water storage capacity is a significant matter for distributed hydrological model.In this paper,the free water storage capacity,a parameter that has a significant effect on the simulation results of model,was se-lected as a research object.We have established the function relationship between topographic index and free water storage capacity to get the spatial distribution of free water storage capacity.And then this method has been applied in Chenhe Catchment which is located in Shanxi Province.Its spatial distribution of free water storage capacity could be derived by the method.A distributed mod-el,Grid-Xin'anjiang model,is obtained based on the spatial distribution of free water storage capacity.Application of the model to the Chenhe Catchment in Shanxi Province shows that this method is effective.This method,based on the laws of physic,can calcu-late the spatial distribution of free water storage capacity with higher accuracy.Thus,it provides a solid basis for development of a distributed model.