Liquid sloshing is prone to occur in liquid cargo ships under the action of wind and waves, and the impact generated by the sloshing will damage the compartment structure, which is one of the important factors inducing safety accidents. Therefore, it is crucial to understand the sloshing phenomenon and propose an efficient anti-sloshing structure. In this study, a new type of floating baffle is proposed, which can provide a better anti-sloshing effect under different filling rates compared with traditional fixed baffle. Sloshing under high-risk filling rate is investigated by numerical simulation based on STAR-CCM+, focusing on floating baffles with different sizes and angles, and the optimal structure of the baffle is selected by analyzing the wave surface displacement, baffle velocity, wave profile, and fluid flow pattern with velocity vector magnitude. The results show that floating baffle can effectively suppress the sloshing by coupling various sloshing mechanisms, its web can cut the free liquid surface in time to suppress the sloshing, and the end of its bottom flange can generate vortex to effectively dissipate the fluid energy, and the heave motion of the baffle can change the trajectory of the fluid mass point under the free surface to reduce the impact on the compartment wall, which further enhances the anti-sloshing effect.