To analyze the nearshore motion characteristics of weakly inertial plastic particles, physical wave flume experiments were conducted to observe and compare the motion characteristics of medium-sized spherical plastic particles in a floating state and bottom-lying state under the action of regular waves with limited water depth. In addition, the dynamic responses of these plastic particles under different wave conditions and boundary conditions were investigated. Based on the motion quantity spectrum, the maximum possible horizontal displacement of the plastic particles in the bottom-lying state during random motion was estimated. The experimental results show that the motion law of plastic particles in the floating state basically conforms to the second-order Lagrangian drift theory; the motion trajectories of plastic particles in the bottom-lying state are mostly irregular, and random high-frequency disturbances account for 20% of their motion amplitudes; the maximum possible horizontal displacement increases first and then converges with the increase in the incident wave period.