Abstract: Boundary conditions is an important research topic in the practical application of computational fluid dynamics. A new Lagrangian boundary conditions framework is constructed by characteristics method using time-line interpolation and is applied in SPH. Compared with methods within Euler framework this method is obvious and easily carrying out for the same formulations in inflow zone and in outflow zone whether for subsonic flow or supersonic flow. SPH numerical simulation in various wave inputs shows the feasibility of the method.