A D-type photonic crystal fiber (PCF) sensor based on surface plasmon resonance (SPR) principle is designed. In order to excite the SPR effect, a gold film is plated on the open-loop channel of the sensor, the free electrons in a metal are resonated with photons. The structural parameters are fine-tuned and the sensing performance of the sensor is studied. The results show that the maximum spectral sensitivity reaches 18 000 nm/RIU in the refractive index range of 1.24—1.32, and the maximum resolution is 5.56×10^-6 RIU. The novel structure with high sensitivity and low refractive index provides a new perspective for fluid density detection.