Cover concrete quality is very important for marine structures, which determines the beginning time of reinforcement corrosion and the life of the structure. The very early age continuous moisture keeping is essential for cover concrete properties develop; otherwise the long-term performance will be reduced heavily. There are many moisture keeping curing methods, but the drawbacks of traditional curing methods make them confined to use in marine environment concrete structures. A kind of moisture keeping membrane which can absorb and hold 100～5000 times of dead-weight water, and impede water evaporating outside with polyethylene film. The results of mercury intrusion porosimetry test and scanning electron microscope show that the new curing product can improve the concrete density decrease the connection degree of pores and the quantity of harmful pores content. Compared with other product on sales, the wet-keeping time can be adjusted and can be used repeatedly and continuously are the distinguishing features, which make it popular in some marine projects.