A plasmonic waveguide coupled system that is composed of a square ring cavity and a metal-insulator-metal (MIM) waveguide with two silver baffles is proposed.The transmission and reflection properties of the proposed plasmonic system are investigated numerically using the finite element method.The normalized Hz field distributions are calculated to analyze the transmission mode in the plasmonic system.The extreme destructive interference between light mode and dark mode causes plasmonically induced reflection (PIR) window in the transmission spectrum.The PIR window is fitted using the coupled mode theory.The analytical result agrees with the simulation result approximately.In addition,the PIR window can be controlled by adjusting structural parameters and filling different dielectric into the MIM waveguide and the square ring cavity.The results provide a new approach to designing plasmonic devices.