Abstract: The digital elevation model (DEM) grid size has significant influence on topographic index,and the effects of topography on watershed hydrology are represented in the TOPMODEL as the distribution of topographical index ln (α/tan β).In this study,the 10 m grid size is selected as the base resolution,and 17 DEMs are generated ranging from 10 m to 1000 m resolutions.The discharge of TOPMODEL in 10m grid is taken as the observed value compared with the discharges among different DEM resolutions.A significant change of the model in response to scale is identified with the grid size of 300 m,the efficiency remains approximately constant between 10m and 150 m,and above this scale the efficiency declines rapidly.In the last section of the study,the Monte-Carlo method is used to analyze the effects of DEM grid size on the five TOPMODEL parameters.More significant are the results of T₀ which shows a strong positive relationship with the grid size increase and the other parameters perform have no clear influence.