Metamaterial perfect absorbers operating at resonance wavelengths have emerged as a promising platform for next-generation optical sensing technologies. In this study, we propose and investigate a high-performance plasmonic absorber designed for refractive index sensing in the infrared region, based on a Fabry–Perot resonance cavity. The structure consists of a thick gold layer acting as a reflective mirror and absorber, while carefully selected dielectric silicon strips are used to achieve optimal resonance coupling. The main innovation lies in integrating a Fabry–Perot resonance cavity with a plasmonic absorber to achieve near-perfect absorption and precise wavelength tunability. This approach improves the sensing accuracy and efficiency compared to traditional absorbers by leveraging strong resonance coupling and optimized material configuration. By varying the refractive index of the dielectric spacer material between the Fabry–Perot mirrors, the sensor demonstrates a clear and measurable shift in resonance wavelength. The proposed design achieves a high sensitivity of 993.03 nm/RIU, an exceptional quality factor of 1581.96, a figure of merit of 958.49 , and near-perfect absorption reaching 99.5 %. These results highlight a significant improvement in sensing performance compared to conventional designs and suggest strong potential for applications in highly sensitive metamaterial-based optical sensors. The proposed structure significantly enhances sensing performance by achieving a higher sensitivity, quality factor, and figure of merit compared to conventional plasmonic absorbers. These advancements make the design well-suited for real-world applications in optical biosensing, environmental monitoring, and infrared detection technologies.