The traditional thin section grinding method would cause the adverse effects on the judgment and i- dentification of bioclastics and package grains bearing in the carbonate rocks. Through repeated experiments, it was found that when the thickness among 0.033 - 0,045 mm, microstructures of bioclastics and grained elastics were clearly shown, which favored accuracy naming and causing analysis. Combining With the requirements of in- terference color on thickness of the thin section, an available thickness control system of carbonate rocks was sug- gested.