In this article, we propose and study a D–shaped plasmonic refractive index (RI) sensor. The numerical simulation is performed by the finite–element method (FEM). Results indicate that the proposed RI sensor is particularly proper for sensing in the wavelength range of 0.5 to 0.7 μm. When the analyte RI varies from 1.33 to 1.36, the highest wavelength sensitivity of 9500 nm/RIU and RI resolution of 6.5 ×10–6 RIU are obtained. Besides, the highest amplitude sensitivity of 215 RIU–1 is achieved with a high linearity of 0.99862. These results confirm the capability of the proposed sensor for rapid and accurate detection of RI change in biological and industrial applications.