In this paper, the authors present results applying a numerical model to simulate hydrodynamics and wave attenuation in the mangrove forest in coastal zone of Bang La - Dai Hop (Hai Phong). Base on Delft3D model and bottom friction formulas of Baptist (2005) and Collins (1972), scenarios in the case of mangrove and without mangrove were setup. The results gained show: current velocities in the mangrove area have decreased about 40-70 percent comparison to in the case of without mangroves. Current velocities in the mangrove forest with in case of normal and small typhoon condition are almost below 0.1 m/s and 0.15 m/s (for big typhoon). Maximum wave height after mangrove forest in the normal condition only reach to 0.1-0.15 m. Wave reduction coefficients are not so much change between different cross-section and their value about 0.20-0.45 (dry season) and 0.3-0.60 (wet season). In the case of small typhoon, maximum wave height after mangrove forest about 0.6-0.8m, wave reduction coefficients value is about 40 percent. In the case of big typhoon, maximum wave height ajter mangrove forest about 0.8-1.1 m, wave reduction coefficients value is about 0.28.