In a traditional network, it is difficult to deploy new network protocols and services, and this problem could not be overcome by itself. Active networking, however, is a feasible way. In this paper, the authors introduce a new router operating system——TH-AOSR (Tsinghua active operating system for router), based on the investigation of active network. In addition to be compatible to traditional routers, TH-AOSR has active networking and active computing capacity, which enables any specific user or application to customize their services, while forwarding data packets securely and rapidly.