Single point diamond turing (SPDT) technique is widely employed in ultra-precision machining of optics. However, the inherent tool marks with strong periodicity induce scattering effects of turned surfaces, significantly deteriorating the optical performances. To suppress the scattering and accordingly achieve optical surface with high quality, the bonnet polishing method is adopted herein to actively modify structures of the residual tool marks. Taking advantage of the Taguchi experiments where the roughness and the power spectral density (PSD) of the polished surface are served as the improving criteria, the optimal polishing parameters are obtained. Polishing experiment is conducted on a fine turned surface by adopting the optimal parameters. The results indicate that the roughness Ra reduces from 3.81 nm to 1.42 nm and the PSDs of surface errors in all the spatial frequencies are also significantly reduced. In addition, the inherent scattering fringes of the original surface are well eliminated, demonstrating the efficiency of the polishing method as well as the optimization method.