The regimes of superfinishing vibropolish of single-crystal synthetic diamond substrates have been optimized. It has been established that after polishing for 100 h the surface roughness was 0.43 nm. A method for controlling the structural perfection of the near-surface layers of diamond substrates upon their grinding and polishing has been proposed and substantiated. X-ray diffraction studies point to the possibility of using the given method in selecting suitable substrates for the technology of growing diamond films in micro- and nanoelectronics.