Cylindrical plasmonic microcavity structure is considered. The system consists of a cylindrically curved metallic structure placed above the flat metallic surface, supporting Surface Plasmon Polariton (SPP) propagation, and they are separated by dielectric gap. The active coupling between SPP resonant modes and SPP modes propagating over the flat metallic surface is demonstrated. The excitation efficiency dependence on structure's geometric and electrodynamics parameters of plasmonic microcavity is investigated. The possibility of controlling (or modulating) resonant SPP modes by varying different parameters such as minimal distance between cylindrical metallic and flat surfaces, relative permittivity of the dielectric gap, as well as working wavelengths are shown. The quality factor of metallic (as the metal is chosen gold: Au) cylindrical plasmonic microcavity is estimated Q ≍ 90, for fixed values of working wavelength: λ0=690 nm, relative permittivity of the dielectric media ∊<strong>d</strong> =3, and the radius of cylinder R=2.5 μm. Considered structure shows strong dependence on the relative permittivity of the dielectric media, the change of third decimal of ∊<strong>d</strong> brings to the significant change (up to three times) of microcavity excitation efficiency. Such phenomena can be successfully used for sensors construction based on plasmonic structures.