In this paper, we address the issue of jamming attacks in the field of maritime communication and propose the application of reconfigurable intelligent surfaces (RISs) in anti-jamming communication at sea. The RIS is installed on an Unmanned surface vehicle (USV) to construct a RIS-assisted USV relay communication system, which mitigates jamming attacks while enhancing legitimate transmissions. Compared to traditional static RIS, the use of mobile USV with RIS enables better performance and greater flexibility. We jointly optimize the trajectory of the USV, the passive beamforming of the RIS, and the source power allocation for each time slot based on proximal policy optimization (PPO), aiming to maximize the average downlink throughput. Simulation results demonstrate that the deployment of RIS on USV effectively suppresses jamming attacks and protects legitimate transmissions.