Abstract: A new method based on geographic information system (GIS) is presented to generate body-fitted meshes automatically.First,a principle is put forward to express the variable flow direction numerically in close approximation,which is based upon the spatial relationship between nodes of the river centerline; then,sections vertical to the flow direction are partitioned throughout the river,and a smoothening method is worked out to prevent overlapping sections from coming into being.A uniform relationship between the sampling direction and the flow direction at anywhere should be guaranteed in order to eliminate "wresting" phenomena in output results and the "right-hand" rule is applied here.And then,an elevation-based interpolation algorithm is designed to reconstruct the landscape model of the river,which is in the form of the output body-fitted meshes.At last,results and tests of the algorithm in pictures and tables are also provided,which proves the algorithm to be well body-fitted and efficient.