A novel approach for measurement of refractive index based on analysis of surface plasma resonance (SPR) spectrum is proposed. It is found that the variety of liquid characteristics will lead to the change of refractive index sensitivity of SPR spectrum. According to the different range of refractive index, resonance wavelength and resonance intensity can serve as measuring parameters, respectively. The refractive index resolution can reach 10-5 theoretically by using this method. Based on theoretical analysis and experiment, a reflective optical fiber SPR sensor system based on resonance light intensity interrogation is designed and demonstrated, and the ratio of sensing signal and reference signal is used as the measurement value of refractive index. In the refractive index range of 1.3325～1.3991, the measurement value decreases with the increase of refractive index, with a linearity of 0.9983. In addition, the coupling coefficient, which can be used to estimate intensity and change trend of SPR effect, is researched.