The research on MAC protocol is one of the key tasks of the underwater acoustic network. In this paper, the author used the simulation tool OPNET to research about the performance of the protocols ALOHA and MACAW in the underwater acoustic network, and compared the network performance in the different traffics, such as, the average delay, the throughput and the energy consumed. The simulation results showed that the performance of the MACAW protocol was better than the ALOHA protocol in the current underwater networks, and both of them can be used in the low traffic network.