In this paper, a novel photonic crystal fiber (PCF) refractive index (RI) sensor with an ultra-wide detection range based on the surface plasmon resonance (SPR) effect is proposed. By selectively filling the air hole with the analyte and introducing the gold-coated air hole, the high performance RI sensing can be achieved. The simulation results show that the asymmetric structure of the PCF makes the x-polarization (x-pol) and y-polarization (y-pol) core modes have different sensing characteristics. The average wavelength sensitivity of the proposed SPR-PCF RI sensor can reach − 4523 nm/RIU in the RI range from 1.25 to 1.45 for the x-pol core mode as well as − 4851 nm/RIU in the RI range from 1.25 to 1.49 for the y-pol core mode. The maximum amplitude sensitivities of − 1239.19 RIU−1 and − 1633.54 RIU−1 for the x-pol and y-pol core modes are also achieved. Moreover, the proposed SPR-PCF RI sensor can obtain the maximum resolutions of 1.603 × 10−5 and 1.695 × 10−5 RIU and figure of merits of 226.92 and 105.76 RIU−1 for the x-pol and y-pol core modes, respectively. It is believed that the proposed SPR-PCF RI sensor has potential applications in the chemistry, biology, and environment monitoring.