In this paper, in case of fractal properties of river bed and the calculation method of fractal dimension, the fractal principle, technology of Geography Information System (GIS) and theory of river bed evolution were combined. Firstly, the attitude data was automatic extracted from the underwater geographical map by the programming, and the GIS software was used to build the river bed surface DEM. Then the Projection Covering Method was improved to calculate fractal dimension of the bed surface with the DEM. At last, the physics conception was discussed by the comparison among the fractal dimensions of each reach in different periods. This research show that this calculated method is effective and accurate, and supplies a new way to calculate fractal dimension of bed surface. Meanwhile, the bed surface fractal dimension varies with the time and space. It can be used to describe the undulating degree of bed scouring and sedimentation quantitatively, and the fractal dimension is correlation with river regime and pattern. This method and conclusion are valuable to river evolution and river mechanics.