The D-type photonic crystal fiber (PCF) refractive index sensors, the multi-core porous PCF surface plasmon resonance (SPR) refractive index sensors with a large dynamic refractive index measurement range, and the dual-channel SPR-PCF refractive index sensors are introduced. Their advantages are summarized and their inherent limitations are analyzed. The SPR-PCF sensors are expected to make breakthroughs in the technical fields such as biomedical testing, food safety testing, mine exploration testing, and environmental chemical testing.