Underwater sensor network has been burgeoned as an interesting research area which has to face a couple of challenges to provide scalable and efficient routing services because of its unique characteristics. In many aspects, it differs from the ground based terrestrial sensor network, Firstly, In UWSNs, acoustic signal is used instead of radio-frequency that attenuates much in underwater environment in comparison with radio-frequency channels. Acoustic channels attribute much lower bandwidth and the propagation speed of acoustic signals in water is several of magnitudes longer. Secondly, nodes of underwater sensor networks move with water current which results dynamic topology. Thirdly, underwater sensor networks consume more power than terrestrial networks due to the underwater channel characteristics and it has high error probability because of acoustic underwater channels' sensibility in noise, multi-path and Doppler spread. Some routing protocols have been proposed to deal with these challenges. But most of these protocols espouse the greedy technique to forward packets to the neighboring node which consumes a lot of energy when network is dense. In this thesis, we propose a Priority Metric Based Ad hoc Routing Protocol for UWSNs. The leading advantages of the protocol are that it consumes less energy in dense network as only one neighboring node needs to capture the packet and process it and it guarantees less number of packet loss in high mobile node environment. Extensive simulation is executed to attest the competence of the proposed routing protocol. The result and analysis bear the indication of the proposed routing protocol's surpassing the existing routing protocol in terms of total energy consumption and average end to end delay.