In order to achieve high-sensitivity monitoring of drugs and chemical materials with low refractive index, a surface plasmon resonance (SPR) sensor with gold film plated in an open loop is designed based on the D-shaped photonic crystal fiber (PCF). The finite element method is adopted to systematically investigate the effects of open loop radius, the distance between the D-shaped structure and fiber core, and the thickness of gold film on the wavelength sensitivity of the proposed sensor. The results reveal that the maximum wavelength sensitivity of the PCF-SPR sensor reaches 15346 nm/RIU (RIU is refractive index unit) when the refractive index of analytes ranges from 1.28 to 1.32, and the corresponding resolution is 6.52×10^-9 RIU. In view of the existing researches, the wavelength sensitivity and resolution of the proposed PCF-SPR sensor are 1.28-6.67 times and 153/1000-783/1000 of that of typical available PCF-SPR sensors within the same range of refractive index, respectively. Therefore, the proposed PCF-SPR sensor can be widely applied in fields such as biomedicine, food safety, and material monitoring.