The hydrodynamic characteristics of perforated caissons are significantly influenced by the viscous fluid motion near the perforations on the front wall. Consequently, models designed in accordance with the Froude similarity suffer from the scale effects. To investigate the scale effects, a Smoothed Particle Hydrodynamics (SPH) model is established, in which fluid motion is governed by the continuity and Navier-Stokes equations, and the solid boundaries are represented by the dynamic boundary particles. The convergence and reliability of the SPH model are examined by employing it to replicate two laboratory experiments. Subsequently, the SPH model is applied to the study of interactions between regular waves and perforated caissons with different length scales, porosities, and chamber length to wavelength ratios. This enables an analysis of the scale effects on the vorticity and velocity fields, wave reflection, and wave force. The findings indicate that a scaled-down model tends to underestimate flow field intensity and wave force amplitude, while overestimate the wave reflection coefficient.