In order to study the stress distribution and dynamic response of concrete dams under underwater explosion impact load,the numerical analysis model of dam structure explosion was established by using ANSYS / LS-DYNA software,including explosive,water medium,air medium,dam concrete and rock.The dam with a bottom width of 60 m and a height of 85 m was selected as the research object.Considering the influence of large deformation and high strain of concrete under explosion load,HJC(Holmquist Johnson cook) constitutive model was used to simulate the damage,failure and plastic deformation of the dam concrete.The possible failure modes and mechanisms under the conditions of two models with and without considering gravity were studied.The stress distribution of the dam after explosion was obtained by numerical simulation,and then four typical locations were selected to study its displacement-time history and pressure-time history.The research shows that the notch generated at the initial explosion is the starting point of shock wave diffusion,and the shock wave will be reflected by multiple times.The maximum stress at the initial explosion can exceed 50 MPa,and then vibrates between 10~30 MPa.The maximum peak pressures appear at the first reflection for all the typical positions,and the first reflection pressure can be used as the explosion impact load of the arc panel.The maximum von Mises stresses occur at the notches near the explosion source and the dam slope corners,which are prone to stress concentration.The displacements of the typical positions are negatively correlated with the distances from the explosive position.The displacements and pressures caused by gravity can resist the explosion responses,but there is no significant difference in the maximum von Mises stress.