Focusing on F1 weathered trough which has maximum water inflow and great difficulty in construction in Xiamen Xiang'an Subsea Tunnel,full-sectional grouting reinforcement and waterproofing,5 m grouting inside heading, 70 m along longitudinal direction of tunnel and superfine cement single-fluid grouting as major grouting material were applied according to poor geological conditions and the character of sudden water inflow. Meanwhile,the corresponding parameters of grouting were established after drillings for grouting were conducted. The results of field monitoring and numerical calculation during construction show that the grouting-effect meets the qualifications of design and construction of Xiamen Xiang'an Subsea Tunnel. The research results can provide technical reference for similar projects in grouting and waterproofing.