On the basis of introduction to the basic theory of TOPMODEL and in view of topographic index algorithm,runoff generation mechanism,and flow confluence method utilized in the current TOPMODEL,we present an improved TOPMODEL for overcoming several problems met in watershed hydrologic modeling as current TOPMODEL is used.For investigating and examining the applicability of the model in different watershed scales and different climatic conditions,the improved TOPMODEL is applied and examined for two different typical watersheds,namely the small-scale Ziwu River watershed in humid area and the medium-scale Malian River watershed in semi-arid area,with the research focus mainly on quantitative analyses of the hydrological processes.The study indicates that the improved TOPMODEL can accurately express the spatial distribution characteristics of the important topographic parameters of real watershed and objectively describe the inner mechanism of watershed hydrological processes.The improved TOPMODEL gives rise to better testing results in small-scale humid watershed.Though a relatively lower accuracy of simulation is obtained in medium-sized semi-arid watershed,the improved TOPMODEL can still simulate and interpret the most mechanisms of hydrological processes of the watershed.