To enhance the data transmission efficiency of underwater optical base stations and multiple user terminals, a spatial division-carrier sense multiple access/collision avoidance (SD-CSMA/CA) protocol incorporating location information is proposed. Considering the inherent directional characteristics of light beam propagation in a straight line, this method enables spatial multiplexing at the optical base station (OBS) by utilizing location information, subsequently increasing independent channel windows to reduce the probability of inter-user collisions. Compared with traditional carrier sense multiple access/collision avoidance (CSMA/CA) protocols, this approach improves user access efficiency and enhances the throughput of the communication system.