Transport of mesoscale particles due to driving flow fields or external forces on a periodic surface appears in many areas. Geometrical and physical characteristics of particles affect the velocities of the particles in these periodic landscapes. In this paper, we present a numerical simulation based on solving the Langevin equation for the meso-size particles subjected to the thermal fluctuations in a periodic array of optical traps. We consider the real-size particles which cause the partial trapping of particles in the optical traps. The particles are sorted for the size-dependency of particles’ trajectories. Our results are in good agreement with experiments.