Plasmonic nanocavity is widely used for enhancing light-matter interaction. Here, an efficient plasmonic nanocavity of the cube-plate system is constructed for the fluorescence enhancement of rice-like CdSe/CdS nanorods (NRs) with tunable emission wavelength. Over ten thousand times fluorescence enhancement is achieved with the assistance of the plasmonic nanocavity. Additionally, a small splitting effect is observed in both photoluminescence and scattering spectra of the NRs in the nanocavity owing to the intermediate coupling effect between the NRs and plasmonic nanocavity, which provides a potential application for optical signal enhancement and strong light-matter interaction.