MPS(Moving Particle Simulation) and SPH(Smoothed Particle Hydrodynamics) methods have some serious drawbacks for pressure solution. The pressure field shows spurious high fluctuation both temporally and spatially. One of the reason why the pressure fluctuation is occurred is that free-surface particles are not recognized accurately. The other is the approximation of the partial differential operators. MPS and SPH methods employ a pre-defined kernel function in approximation of the gradient and Laplacian operators. Since the kernel function is constructed artificially, an accurate solution cannot be guaranteed, especially when the distribution of particles is irregular. In this study, we propose a particle simulation method based on the moving least-square technique for solving the partial differential operators by Taylor-series expansion. The developed method was applied to the hydro-static pressure and dam breaking problems for its validation.