Surface plasmon excitation is dependent on the complicated refractive index of the metal, the thickness with optical characteristics of the metallic layer, and the angle of the incident light. MATLAB was employed to model the proposed multilayer system and to determine the conditions under which surface plasmon resonance (SPR) occurs, to evaluate its effectiveness as a sensor for detecting small variations or contaminations in the sensing medium. The proposed configuration consists of three layers: a thin tin selenide (SnSe) layer with a thickness ranging from 10 nm to 80 nm, a silver (Ag) layer with a fixed thickness of 50 nm, and a molybdenum disulfide (MoS₂) layer with a thickness varying from 10 nm to 80 nm in increments of 10 nm. The structure is deposited on a BK7-type glass prism using water as the sensing medium, where the refractive index variation (Δn) was considered of (0 and 0.01). Simulations were performed over a wavelength range of 100–1000 nm, in steps of 100 nm. To evaluate the surface plasmon resonance characteristics, reflectance (R) was plotted as a function of the incident angle (θ). The results improved SPR characteristics, including a sharper resonance dip, reduced full width at half maximum (FWHM), and enhanced resonance extent (Ld). The proposed SPR sensor achieved high sensitivity of 230°/RIU for Δn = 0.01 at λ = 800 nm, with d(MoS₂) = 40 nm and d(SnSe) = 0 nm, indicating strong performance in the infrared region. Additionally, variations in MoS₂ thickness exhibited a slight influence on the resonance angle due to the refractive index of the sensing medium. The observed shift in the R‒θ curve demonstrates the great stability and sensitivity of the developed SPR sensor in the near-infrared spectral range, confirming its capacity to detect minor changes in refractive index in aqueous environments.