Abstract: The surface of alumina ceramics was polished by chemical mechanical polishing process. Combined with the arithmetic mean height of Sa and root mean square height of Sq, the variation in Ssk（skewness） and Sku（kurtosis） with polishing time were analyzed to reveal the formation mechanism of smooth surface. The results show that Sa and Sq decrease rapidly first and then slowly with the polishing time increasing, while Ssk decreases first and then rises and then fluctuates, and Sku rises first and then falls and then rises. The three mechanisms of plastic removal, grain fracture and intergranular fracture are key factors that affected the surface state of alumina ceramics. The plastic removal affects the height distribution of the surface in the whole polishing process, which is beneficial to build smooth face. The grain fracture and intergranular fracture play an obvious impact on the height distribution, which are the main cause of fluctuation of Ssk and Sku at the later of polishing.