A transparent boundary condition was developed for calculating water waves propagating to a distant area by using a particle method. In front of the boundary, the incident waves were analyzed by Fourier analysis, and the particles on the transparent boundary were forced to move to absorb the incident waves. The characteristics of this study are to introduce the technique of wave analysis used for the wave tanks to the particle simulation and to reduce the calculation cost by employing an inflow and outflow boundary. Water waves were calculated in two wave periods by the developed transparent boundary condition. As the results, it was shown that this transparent boundary transmitted the incident waves without the reflection waves. It was also shown that the calculation cost was smaller than that of the ordinary high viscosity boundary condition.
