In 6G, high data rate services are expected to be provided for marine users. However, it’s challenging to design an efficient maritime wireless communication system due to the limited bandwidth and harsh marine environments. In this paper, a reconfigurable intelligent surface (RIS) assisted millimeter-wave (mm-Wave) multiple-input multiple-output (MIMO) system is proposed for maritime wireless communications. Specifically, the RIS is carefully designed according to the maritime wireless channel conditions, where singular value decomposition based alternative optimization is considered. Then, in order to improve the system performance, a receive beamforming scheme is proposed by considering a weighted adaptive strategy for iteratively mitigating the multiuser interference. With the aid of our proposed algorithm, a robust multiuser interference mitigation can be achieved by offering a versatile solution for multiuser interference issues in the RIS-assisted mm-Wave MIMO system. Finally, simulation results are provided, showing that an improved system performance can be attained by the proposed RIS assisted mm-Wave MIMO system for maritime wireless communications.