The invention provides a method for preparing a silicon carbide chemical mechanical polishing solution with improved pH stability. The preparation method comprises the following steps: performing surface modification on a high-hardness grinding material dispersion solution by using a surface modifier, and successively adding a pH stabilizer and an oxidant, wherein the surface modifier is organic acid. The stability of the pH value of the polishing solution can be well kept in the chemical mechanical polishing process, and the polishing solution is good in dispersion stability and uniform in dispersion. Since the pH stabilizer is added into the preparation method of the polishing solution, the pH value stability of the polishing solution in the chemical mechanical polishing process is higher, the organic acid surface modifier in the polishing solution is used for performing the surface modification on the high-hardness grinding material dispersion solution, so that the polishing solution is unlikely to have hard agglomeration. The polishing solution of the invention is pollution-free to the environment, and can be used in a circular feeding way.