The surface plasmon resonance (SPR) of the refractive index (RI) sensor based on a Multiple D-shaped Au/Fe3O4 Nanowire is presented in this paper. This designed sensor uses magnetite (Fe3O4) as the sensing layer, coated on the multiple D-shaped gold nanowires (AuNWs) to stimulate the plasmon mode. The key sensing mechanism is the interaction between the fundamental fiber guided mode and plasmonic modes of optical fibers, which results in the formation of various resonance peaks depending on the analyte RI. Finite-Element Method (FEM) based COMSOL Multiphysicsis employed to analyze the surface plasmon properties. By optimizing the performance key parameters of the proposed sensor, the radius of the AuNW and the thickness of the magnetite sensing layer on sensor sensitivity (S) are optimized. Simulation results indicate enhanced sensitivity at 8.5µm/RIU. The resolution is 1.17 ×10⁻⁶ RIU in the sensing RI range of 1.33 -1.39. The results indicated that the proposed plasmonic sensor-based multiple D-shaped AuNWs with Fe3O4 nanomaterials structure has potential biosensor applications.