This paper presented a new MANET accessing Internet model. In this model, the benefits of three nodes-the source node, gateway node and decision node, were considered synthetically, and gateways were arranged and selected according to the real-time state of accessing network. Otherwise, it simulated the pheromone's update process in ant colony algorithm and computed transmission probability according to the pheromone density on the link, link bandwidth and delay, which are found in searching route. When the gateway pheromone was calculated, it would be added to RREQ. This model was simulated by NS 2. The test result indicated that though it increased average delay, it reduced routing overhead effectively and increased packet delivery radio. The validity of algorithm is validated.