Owing to their broad applications and huge potentials, Underwater Acoustic Networks (UAN) have drawn growing interests from researchers of science, industry and government. The complex underwater environment and unique acoustic channel lead to the difference between UAN and traditional RF Ad Hoc networks. This paper studies the performances of UAN based on Dynamic Source Routing (DSR) utilizing OPNET Modeler. Simulation results show that traditional DSR causes the incredible phenomenon of much more received packets at destination than packets sent from source in UAN. Based on the features of UAN and acoustic channel, a revised DSR is proposed in this paper. The revised DSR not only resolves the problem of much more received packets than packets sent from source in UAN, but also enhances the performances of UAN in delay and routing overhead. The complex underwater environment and unique acoustic channel not only affect physical layer performance but impact the protocol design on data link layer and network layer of UAN.