A novel type of polymethyl methacrylate (PMMA) fiber refractive index sensor based on surface plasmon resonance (SPR) is proposed in this work, which is applied to measure the refractive index of liquid. The performance is investigated by the SPR theory and the structural properties of the side-polished D-type fiber. In order to obtain the optimized parameters of SPR sensor, the effects of metal film material, the metal film thickness and the length of the sensing zone on spectral characteristics of the sensor are studied. The fiber SPR sensor is manufactured and applied to the preparation experiment. The change of refractive index of glycerol solution is detected and analyzed at a constant temperature of 20 °C. Experimental results indicate that the proposed fiber SPR sensor exhibits refractive index sensitivity up to 3328.1 nm/RIU in the range of 1.334–1.388, which can be utilized as the alternative material for bio-sensing studies.