In this paper, we study photon emission of single “silicon-vacancy” centers in HPHT-nanodiamonds on 1) a gold surface and 2) inside nanophotonic cavity which is cylindrical nanopit on a gold film. It was found that the saturation intensity of single SiV centers in the nanocavity increases by up to 3 times compared to similar diamonds on the gold surface, along with a twofold decrease in saturation power and a 15% reduction in lifetime. The obtained results are explained by the interaction of SiV centers with the surface plasmons in cylindrical nanopit in gold film, as well as by the narrow directivity of the emitter related to geometry factor of the plasmonic nanocavity.