The present invention discloses a route diffusion method for dynamically generating expansion tree in the network, specifically suitable for the scene of broadcast routing in an Ad hoc Network or a Wireless Mesh Network. The invention takes route cost and hop together as criterion to select an optimum route, and every node in the network uses the flooding of the call packet to establish, update and delete the corresponding node in the broadcast tree. The method includes: broadcast tree generation, wherein, network nodes select and determine father nodes according to the hop of packets for reaching interactive root nodes; broadcast tree updating, in the broadcast tree updating process, according to the setting triggering criterion, when reaching the corresponding triggering condition, the broadcast tree updates according to the broadcast tree updating method; and broadcast packet transmit-receive. The route diffusion method for dynamically generating expansion tree in the network adopted by the invention can realize the effective spreading of the broadcast packet, and effectively inhibit the generation of broadcast storm and routing self-loop; the method has relative simple and practical protocol, application in micro scale networking, and fast network convergence rate.