Underwater acoustic (UWA) communications have been developed rapidly in recent years. Their applications are beginning to shift from military towards commercial. With the development of the UWA communication, more and more attentions are high speed transmission and high reliability transmission, especially the latter. In the channel of UWA, due to the multipath caused time delay spread. The multipath time delay spread not only limit the channel frequency band, but also leading to Inter-symbol Interference (ISI), constraint the transmission performance of system. In order to reduce the ISI and increase the transmission performance of system can use the adaptive equalizer to reduce ISI. In this work, image transmission performance of UWA communication systems focuses on Binary Frequency Shift Keying (BFSK) in water, and the ways to remove ISI caused by multipath. We will adopt adaptive equalizer that based on LMS (Least Mean Square) algorithm to improve the transmission performance of system through simulation and experiment.