This paper presents a method for high-dimensional information modulation and demodulation using a vortex beam for underwater wireless optical communication by identifying the superposition state of orbital angular momentum in the vortex beam. The method and process of identifying the superposition states of two vortex beams are described. The topological charge numbers in the superposition states are obtained based on the light intensity distribution diagram of the superposition states after water channel transmission. Based on the results, it is experimentally demonstrated that the superposition state of orbital angular momentum can achieve the modulation and demodulation of 16-dimensional information under low-topological-charge conditions. Thus, this study provides a feasible scheme for applying vortex beams in underwater wireless optical communication.