Right getting hold of the contact form between the wafer and the pad is the precondition of fully understanding the material removal mechanism in wafer chemical mechanical polishing (CMP) process. In this paper, according to friction and abrasion theory, the differentiating method of contact form between the wafer and the pad has been obtained firstly. Then, the material removal rate (MRR) produced by mechanical action, chemical action and their interaction has been achieved by test results of MRR. According to analysis on test results of MRR, it is concluded that the mechanical action produced by abrasives is the main mechanical action, the MRR produced by the interaction between the mechanical action of abrasives and chemical action of slurry is the main MRR and the contact form between the wafer and the pad is solid-solid contact in wafer CMP. These results will provide theoretical guide to further understand the material removal mechanism of in wafer CMP.