Rapid transmission of vector map data over the Internet has become a hot issue in the field of spatial data delivery in web-based environment because of the conflict between huge quantity of map data amount and limited network bandwidth. A method of organizing and transmitting vector river data via the Internet is put forward in this paper. This approach considers two levels of importance of river data, i.e. the importance of river branches and the importance of the points belonging to each river branch, and forms data packages according to the two levels of importance. Our experiments have shown that the proposed approach can reduce 90% of original data as well as preserve the river structure well.