Based on the SWAT model，this paper designs the method of hydrological response unit in the middle and small watersheds based on the Lian River Basin in the upper reaches of the Gan River.Based on the DEM data，using the vector data of TM image and Google Earth as reference，the modal exponential method is used to simulate the fitting of the hydrological basin，and the threshold of river network is determined to ensure the accuracy of river network division.The Lian River Basin is divided into 49 sub-basins and 181 hydrological response units in combination with land use data，soil data and slope data.Based on the division of the hydrological response unit of the Lian River Basin，the inaccuracy of the sub-basin and the hydrological response unit is induced by the artificial experience of the river network，which provides a reference for the simulation of the distributed model of the sub-basin in the upper reaches of the Lian River and the Gan River.