Map generalization is a very important work in processing the compilation of a map because it directly influences the quality of the map. In convention, the compilation work is done by human; therefore, the quality is determined by the compiler's favor in using a specific map generalization method to express the geographic features. Thus, inconsistency between maps can frequently be found due to the lack of a unifed standard for map compilations, causing great inconvenience to the users. In order to control the quality, the computer-aided map compilation is necessary, however, practical generalization rules for different geographic elements shown on a map have to be establish first. Development of these rules thus becomes an important issue to modern cartography. According to our survey, map generalization of contours, settlements and drawing has been studied by many scholars. However, generalization of river networks on a map is seldom studied. Since the river network is a also an important geogrhic element of maps, a study on this subject is then of the great interest. The present study is conducted on the basis of Horton's stream ordering and Topfer's principle of the selection. To derive a generalization rule for river network s shown on maps of different scales, the basin of Mukua Hsi and Shoufeng Hsi in Taiwan have been chosen to be samples to be analyzed. According to the analysis, the generalization model of river networks is then developed, using a statistic regression menthod and is expected to be a practical reference for the devlopment of automatic cartography.