This study presents a high-performance refractive index sensor based on surface plasmon resonance (SPR) in a photonic crystal fiber (PCF). By exciting SPR in the near-infrared band (1.3—2.3 μm), the proposed sensor extends the refractive index detection upper limit for similar SPR-PCF sensors while enabling high-refractive-index sensing. The sensor′s optical loss, SPR characteristics and refractive index sensitivity are systematically investigated using the finite element method (FEM), and its structure is optimized for enhanced performance. Within the refractive index range of 1.44—1.58, the sensor achieves a remarkable sensitivity of 9 100 nm/RIU and a resolution of 1.099×10^-5 RIU. These advancements make the sensor highly promising for applications in environmental monitoring, particularly in crude oil leakage detection.