The invention relates to a chemically mechanical polishing solution and a preparation process thereof, and particularly to a polishing solution containing a ceric oxide powder / colloid silicon dioxide mixed abrasive and a preparing process thereof. The polishing solution containing the mixed abrasive is simple in preparing process, practical and prone to production. Raw materials of the polishing solution comprise 3-10% of ceric oxide powder having a particle size of 100-2000 nm, 5-50% of colloid silicon dioxide having a particle size of 10-200 nm, and 0.001-0.5% of a dispersing agent, with the balance being water. The polishing solution is prepared by selecting a container, adding the colloid silicon dioxide solution, adding the ceric oxide powder, stirring uniformly, adding the dispersing agent and the water to the required volume, and stirring uniformly. The ceric oxide powder and the colloid silicon dioxide of different particle sizes are adopted as the abrasive. In the polishing solution, the smaller silicon dioxide particles decrease scratches, pits, and other defects so as to improve the surface quality, and the larger ceric oxide particles obtain a high removing rate.