A TiO₂ thin film with an optical thickness of λ/4 is plated on K9 glass using the electron beam thermal evaporation technique. The effect and mechanism of different deposition rates and deposition angles on the scattering loss of TiO₂ thin films are investigated. The surface roughness and bidirectional reflection distribution function of the TiO₂ thin film before and after plating are measured using TalysurfCCI white light interference surface profiler and Horos scattering instrument. The results show that the surface roughness of the TiO₂ thin film decreases as the deposition rate increases and eventually reaches 0.88 nm, which is less than the bare substrate surface roughness of 1.5 nm. This indicates that the TiO₂ thin film can reduce the surface roughness of the substrate, and it is capable of smoothing the substrate. As the incident deposition angle increases, the surface roughness of the film gradually increases. When the deposition angles are 0° and 20°, the surface roughness of the film is less than that of the substrate; when the deposition angles are 40° and 60°, the surface roughness of the film is greater than that of the substrate. A positive correlation exists between the amount of surface scattering of the film and the surface roughness. Experimental data agree with theoretical calculations. When the surface roughness of the film is less than that of the substrate, the surface scattering of the film is lower than that of the bare substrate. Thus, TiO₂ thin films can reduce surface scattering from the substrate.