In this paper, the dam-break problem is numerically simulated using two-phase moving particle semi-implicit (MPS) method. Firstly, the two-phase MPS method is extended from single-phase MPS method. The present method treats the multiphase system as a multi-density and multi-viscosity fluid, and a single set of equations could be used for the whole system. The interaction between particles of different phases is considered through the applications of inter-particle viscosity and density smoothing technique. The two-phase MPS method is then successfully applied to violent dam-break problem. The numerical results obtained by single-phase and two-phase method are both compared with experimental results in the open literature. The characteristics of air cavity are analyzed, including the pressure inside the cavity and the cavity shape deformation.