Dynamics model on abrasive particles and workpieces during the centrifugal barrel surface finishing process was built by Discrete Element Method (DEM). The motion status of abrasive particles and workpieces was visually simulated and some important process parameters were numerically studied. The influence of fill ratio on finishing efficiency was analyzed, and finishing efficiency was the highest as the fill ratio is 65%. the simulation results are basically coincident to the experimental results. Both results have proved that filling ratio is the main parameter that changes medium motion laws, which provides an very efficient way to further optimize design parameters and process parameters, as well as to improve production efficiency.