Abstract: Fiber Reinforced Polymer (Fiber Reinforced Polymer, FRP) has the advantages of light weight, high strength, and strong corrosion resistance, and is widely used in the marine field. In order to design FRP with good impact resistance in the shallow sea environment, this paper, aiming at the specific applications of Fiber Reinforced Polymer (FRP) in the shallow sea environment, studies the moisture absorption characteristics, low-velocity impact characteristics, and compression mechanical properties after impact of two different composite material systems, namely Ultra-High Molecular Weight Polyethylene Fiber/Elium Resin (PEFRP) and Carbon Fiber/Elium Resin (CFRP) after degradation under pressure environment. The research results show that the water absorption rate of PEFRP is greater than that of CFRP under the same working conditions. During the low-velocity impact process, PEFRP undergoes plastic failure, while CFRP undergoes brittle failure. PEFRP has more superior impact resistance, but CFRP has a higher damage tolerance. Both types of FRP have a good impact resistance retention rate within 150 days of degradation. The presence of ions has a greater impact on the damage tolerance of PEFRP, and a smaller impact on CFRP. The Elium-based FRP degraded in the shallow sea environment has a certain damage tolerance retention rate in the early stage, and the damage tolerance gradually decreases as the degradation time increases. This may be related to the generation of micro-cracks in the matrix due to water absorption during the degradation process of FRP. This study provides experimental data support for the practical application of FRP in marine engineering by simulating the impact resistance of the two types of FRP in the shallow sea environment and the changes in impact resistance at different days.