Abstract: Yttrium aluminum garnet (YAG) crystal is widely used as gain medium in laser device due to its excellent physical, chemical and optical properties. However, current process can hardly satisfy the requirements of high efficiency and high quality in YAG crystal processing. Based on the material remove mechanism of silica sol, new slurry for chemical mechanical polishing (CMP) of YAG crystal was invented, and its composition was optimized by orthogonal experiment. The material removal rate of CMP was increased to 34 nm/min, and the surface roughness of YAG crystal was 0.5 nm after the CMP process by using the proposed slurry. Compared with the traditional silicon sol, the new slurry improves the polishing efficiency by 240% and reduces the surface roughness by 17%. After comparing the performances of both slurries, the effect of interacting mode at CMP surface on material removal mechanism is proposed.