Surface roughness by peaks and depressions on the surface of titanium dioxide(TiO2/ thin film, which was widely used for an antireflection coating of optical systems, caused the extinction coefficient increase and affected the properties of optical system. Chemical mechanical polishing(CMP) is a very important method for surface smoothing. In this polishing experiment, we used self-formulated weakly alkaline slurry. Other process parameters were working pressure, slurry flow rate, head speed, and platen speed. In order to get the best surface roughness(1.16 ? the scanned area was 10 10 m2/ and a higher polishing rate(60.8 nm/min), the optimal parameters were: pressure, 1 psi; slurry flow rate, 250 mL/min; polishing head speed, 80 rpm; platen speed, 87 rpm. Surface roughness by peaks and depressions on the surface of titanium dioxide (TiO2 / thin film, which was widely used for an antireflection coating of optical systems, caused the extinction coefficient increase and affected the properties of optical system. Chemical mechanical polishing (CMP) is a very important method for surface smoothing. In this polishing experiment, we used self-formulated weakly alkaline slurry. The optimized area was 10 m 2 / and a higher polishing rate (60.8 nm / min), the optimal parameters were: pressure, 1 psi; slurry flow rate, 250 mL / min; 87 rpm.