Based on the principle of Michelson interferometer and the characteristics of fiber optic sensors,this paper has developed a novel single-mode core-offset fiber optic interferometer sensor,and uses it for the refractive index measurement in sugar solution.Experimental results show that when the sensing range is from 1.33 to 1.39,there will be a better progressive decrease relationship between the characteristic wavelength and the refractive index;the refractive index change of 0.01 of the sucrose will lead to an approximate average variation of 0.12 nm in the characteristic wavelength.This sensor can be used for on-line liquid refractive index and concentration monitoring with simple structure and high sensitivity.