A plasmonic triple-wavelength demultiplexing structure based on metal-insulator-metal waveguides side-coupled with nanoring cavities was proposd by studying theoretically and numerically. The structure consisted of three output channels, each of which was sandwiched by two nanoring cavities. By changing the filling medium of the ring and the relative position of the inner and outer circle, the reflection and transmission spectrum of each channel could be dynamically tunable. Finally, according to the reflection and transmission characteristics of three channels, the demultiplex at three telecommunication wavelengths 1 310 nm, 1 490 nm and 1 550 nm with excellent performance was studied. Temporal coupled-mode (CMT) theory and finite-difference time-domain (FDTD) method are applied to simulation and analysis, and this work can find potential applications for on-chip integrated all-optical circuits.