Abstract: In order to further show the underwater terrain terrain evolution mechanism of the Pearl River networks,we employ the techniques of 3-D visualization and spatial analysis.The comparision with 3-D data of different period will help to expose the underwatr terrain evolution and forecast the trend of the evolution of the Pearl River estuary.In addition,in view of the problem of the elevation value rectified,we present the methods of zero value line and the field identification.The method of zero value line is based on that of point radial.But this method exists the disadvantages,such as the extra computation.The method of field identification is proved to be an efficient method.