Abstract: The river networks is a kind of natural fractal. This article discusses mainly how to get the dimension of a river network by counting the boxes which covers the river networks in the mean while by changing the side of the boxes. All of these are based on the MapInfo and MapBasic which can program the computer to do the job instead of manual operation and can get much rare comprehensive information of the dimension of the river networks. By this way,the article points out that the fractal dimension of network is related not only to the development phase of the river but also to the system of physiognomy,land use and so on.