We study the underwater propagation characteristics of orbital angular momentum (OAM) states by experimental method. We build an underwater optical communication system of OAM states, and then discuss the underwater transmission capacity of OAM states by the spread spectra and the probability curves of the original and adjacent OAM states. The experimental results show that the probability of original OAM state decreases significantly with the increasing of salinity, and the propagation probability decreases with the increasing of topological charge interval.