Attenuation effect of artificial mangrove Sonneratia apetala and Kandelia obovata on waves was studied quantitatively through field monitoring at Sanjiang Bay, Dongzhai Harbor, Hainan. The results showed that bare mudflat could only attenuate waves slightly, with 1/10 wave height, 1/3 wave height and mean wave height reduced by 2.9%, 4.4% and 5.8% respectively after the waves traveled 50m across the mudflat. Significant attenuation effect on waves could be seen of both artificial mangrove forests. In general, 1/10 wave height, 1/3 wave height and mean wave height were reduced by 46.3%, 46.4% and 46.1% respectively after the waves traveled 50m across artificial K. obovata forest stand, and the same indexes were reduced by 30.1%, 29.6% and 28.8% respectively on artificial S. apetala forest stand. Larger section area of mangrove forest stand turned to result in higher wave attenuation rate. At shallow water area, attenuation rate of mangrove forest decreased as the water grew deeper. While at the same water depth, attenuation rate of mangrove increased as wave height grew higher. Attenuation rate of mangrove on waves kept a nonlinearly positive relationship with travel distance of the waves. With the extension of waves across mangrove forest, wave height tended to be reduced continually, while the decline rate became less significant gradually.