The power-aware routing protocols are aimed to maximize the system lifetime of the mobile ad hoc networks, since the mobile hosts within the networks are normally power-constrained. We presents a novel power-aware routing protocol called Multi-Route Transmission Routing which utilizes multiple routes to transmit the data traffic simultaneously and leads to a balanced energy consumption distribution. Thus, the proposed routing approach can extend the system lifetime of the networks. A new routing cost metric is also proposed for the route selection mechanism, which takes both the shortest-path and the maximum system lifetime into consideration and dynamically adjusts its weight between them according to the energy usage of the network. Experiment results show that, the proposed routing protocol provides a higher performance than other well-known power-aware routing protocols in terms of the energy-efficiency.