In this study, a numerical method was developed to predict the behavior of wave-dissipating blocks caused by water waves. The method is based on the moving particle semi-implicit (MPS) method [1], the overlapping particle technique (OPT) for multi-resolution simulation of the particle method [2, 3], and the collision and contact model for rigid bodies. The developed method computed the three-dimensional phenomena near wave-dissipating blocks and solitary wave propagation far from the blocks in three- and two-dimensional sub-domains, respectively, by coupling the sub-domains. Each subdomain had its own independent spatial resolution. Water waves were generated and propagated in a two-dimensional sub-domain, and wave-block interactions were calculated in a three-dimensional domain. The three-dimensional domain was composed of middle- and high-resolution sub-domains, and the blocks were placed in the high-resolution sub-domain. This multiresolution based on domain decomposition reduced the number of particles while maintaining the spatial resolution around the blocks. In the three-dimensional high-resolution sub-domain, the energy-tracking impulse method (ETI) [4] was adopted to calculate collisions and contacts between blocks and walls. This method is based on the force product rather than the distance and has the advantage of stable simulations. The friction force acting on the wave-dissipating blocks was also calculated using the ETI method and determined by the friction coefficients. The movements of the wave-dissipating blocks caused by water waves were simulated under various conditions. The results showed that the simulated behaviors of the wave-dissipating blocks were qualitatively in agreement with the experimental results. In addition, the proposed method reduced computation time by approximately 90%. REFERENCES [1] Koshizuka, S.et al, Moving Particle Semi-implicit Method, Academic Press (2018) [2] Shibata K. et al., Computer Methods in Applied Mechanics and Engineering, (2017) 325: 434-462 [3] Toshiki Imatani et al., 15th World Congress on Computational Mechanics (2022) [4] Asai, Mitsuteru, et al., Computer Methods in Applied Mechanics and Engineering 377 (2021): 113681.