The developing behavior of toner particles in a twocomponent development system was simulated to find out the correlation between experimental and simulated results by using large-scale Discrete Element Method (DEM). The effects of developing bias frequency or circumferential speed of photoreceptor on the developed toner mass per area (DMA) was discussed both in experimental and simulation works. The toners were adhered on the outside of latent images under the low frequency, and its mass decreased with increasing the frequency. DMA decreased with increasing circumferential speed of photoreceptor, because the toners had less chances to contact the latent image. The image was also damaged by the magnetic brush under the high speed due to an increase of the shear force. The similar tendency was observed under all conditions, and it was found that the simulation results correlate with experimental ones very well. Therefore, this simulation method is useful for the analysis of the developing behavior in electrophotographic system and the optimization or designing of this system will be possible.