In recent years, most of the previous studies focused on the perfect absorption and high-efficiency quantum memory of the one-sided system, which ignoring the characteristics of its optical switching contrast. Thus, the performance of all-optical switching and optical transistors is limited. Herein, we propose a localized surface plasmon (LSP) mode-assisted cavity QED system which consists of a Λ-shaped three-level quantum emitter (QE), a metal nanoparticle and a one-sided optical cavity with a fully reflected mirror. In this system, the QE coherently couples to the cavity and LSP mode, respectively, which is manipulated by the control field. As a result, considerable high and stable switch contrast 90% can be achievable due to the strong confined field of LSP mode and perfect absorption of the optical medium. In addition, we obtain a power dependent effect between the control field and the transmitted frequency as a result of the converted dark state. We employ the Heisenberg-Langevin equation and numerical Master equation formalisms to explain high switching, controllable output light and the dark state. Our system introduces an effective method to improve the performance of optical switches based on one-sided system in quantum information storage and quantum communication.