Chemical Mechanical Polishing (CMP) is the key technique for wafer global planarization. However, the characteristic of abrasive particle, including particle size and grain/grain collision elasticity, plays an important role in CMP process. This investigation analyzes the slurry flow between the wafer and pad using a grain flow model with partial hydrodynamic lubrication theory. This model predicts the film thickness and remove rate of the slurry flow under a variety of the CMP parameters including load, rotation speed, pad roughness, grain/grain collision elasticity and grain size. The theoretical results compare well with the previous experiment data. This study elucidates the grain characteristics during CMP process. It also contributes to the understanding of abrasive particle effects in the chemical mechanical polishing mechanism.