Chemical mechanical polishing (CMP) is an effective key technology for obtaining high surface flatness, and has been widely studied and applied. The removal of its surface material depends on the actual contact state it is in. The form of polishing pad/wafer interactions is summarized in the paper, including slipping through each other without direct contact, mixed lubrication, and direct contact. The contact state and its influencing factors are analyzed, including the deformation, glaze and wear of the polishing pad, the influence of abrasive particles in the polishing solution, and the change of the thickness of the passivation layer by the surfactant. The research progress of the contact state in chemical mechanical polishing is summarized, including the calculation of the contact area ratio by optical microscopy, the measurement of the contact area ratio of the thin film sensor, the measurement of the thickness of the polishing solution by the dual emission laser induced fluorescence technique, and modeling of material removal rate by polishing surface morphology evolution. The characteristics of these methods and the problems that exist are pointed out in the article. Finally, a new idea of nanogap measurement technology to measure the dynamic change of contact rate in chemical mechanical polishing to obtain the true contact state and contact state transition law is proposed.