The Distinct Cell Model (DCM) for the contact detection in the algorithm of the Discrete Element Method was proposed to improve the calculation speed when particles have a large size ratio. This model has several grids, which are overlapped three-dimensionally, and the particles having different size are boxed in a suitable grid cell. The contact detection time of this model was measured and compared with that of the conventional cell model in the simulation of a rotating dram. The contact detection using the DCM was extremely faster than that of the conventional cell model; e.g. when particles had a size ratio of d(max)/d(min) = 15, the speed-up was about 25. The speed-up ratio increases with increasing particle size ratio, regardless of the number of grids. This model has an advantage of being able to set optimum cell sizes for all particles, thus, the number of searching cells and contact check can be minimized. The optimum cell size of the DCM is the size that each cell has about 1 particle in it when two grids are used, 0.3-0.6 particles in the case of more than three grids. The large-scale simulation of granular flow having a large particle size ratio will be possible by using the Distinct Cell Model.