Liu et al. [Liu, C., Huang, Z. & Chen, W. [2017] “A numerical study of a submerged horizontal heaving plate as a breakwater,” J. Coast. Res.33(4), 917–930.] numerically studied the wave scattering by a heaving submerged horizontal plate (SHP) within the framework of the potential flow theory. They presented the excellent performance of the heaving SHP on wave blocking, because the radiated wave induced by the heave response of plate is likely to neutralize the transmitted wave. As a further study, the present work simulates the wave–heaving SHP interaction using the smoothed particle hydrodynamics, which is widely recognized as a powerful tool for computing complex viscous fluid dynamics. In this way, additional understanding on the wave blocking mechanism of the heaving SHP is contributed. The effect of submergence of plate on the wave and structural dynamics is also investigated. The results show that, under most submergence conditions, a heaving SHP breakwater is more effective than a fixed one. In terms of the limited cases in this research, 17% is proven to be the optimum ratio of submergence to water depth for the heaving SHP breakwater.