Abstract: Abrasive free chemical mechanical polishing can effectively remove the flying cutter pattern remaining on the KDP surface after the KDP fly-cutting. During the polishing process, the KDP and the polishing pad asperities rubber together. There is micro-mechanical effect in the process that affects the final polishing effect. In this paper, the mathematical model of KDP and polishing pad asperities was established. According to Hertz theory, the surface contact stress of KDP crystal during polishing was calculated and analyzed. The polishing pressure, friction coefficient, Young′s modulus of polishing pad and asperity radius of polishing pad were studied. The influence of polishing parameters on the micro-mechanical action was obtained, and the maximum allowable polishing pressure was obtained under different polishing conditions. In addition, the mechanical effects between KDP and polishing pad were further analyzed in combination with the experimental results, and the mechanism of chemical mechanical polishing removal of KDP based on microemulsion was further revealed.