Due to unawareness of network conditions, regular Transmission Control Protocol (TCP) is not able to fully control the limited resources and distinguish packet loss from congestion loss and random loss. Because of such characteristics, the performance of TCP will be downgraded severely if it runs on wireless networks, such as multi-hop ad hoc networks. In an ad hoc network, nodes play both roles of end system as well as router. We take this advantage to propose a new TCP congestion control mechanism by router-assisted approach. Based on the information feedbacked from routers, a TCP sender is able to adjust its sending speed dynamically in order to avoid overshooting problem. Our proposed protocol has 5~10% higher throughput than TCP NewReno and much less number of retransmissions. The fairness is also achieved while our proposed protocol coexists with other major TCP variants.