This paper describes the development of a numerical model and scheme that can accurately solve the particle motion dynamics in microchannels considering the physics of the AC electric field, dielectrophoresis (DEP) force, and hydrodynamic forces in three-dimensional form. To demonstrate the performance of the model, the numerical model was applied to simulate the motion of a particle flowing over the rail-type electrodes. This rail-type electrode produces a DEP field which enables the trapping of the particle at the position adjacent to the channel bottom wall and manipulate it along the electrodes accurately. The numerical results were compared with the experiment measuring the motions of polystyrene particles using a high-speed camera. The experiment results showed that the particles flowing into the electrode area can be trapped successfully, and moreover, the particle will flow steadily with an accuracy of 5% along the rail-type electrodes. The streamwise velocity distributions of the simulation and experiment were compared and the two results agreed reasonably well showing the validity of the present model.