An accurate measurement approach to liquid refractive index of liquids with a fiber-capacitance droplet analyzer is proposed. A linear model between first peak values of liquid droplet fingerprints and refractive indexes is built by the least square method, where the surface tensions of glucose solutions and NaCl solutions are similar to that of water. The refractive index calculation model with surface tension modification is proposed based on the simulation analysis on influence of the surface tensions of ethanol and propanol solutions on droplet shape, where the surface tensions of ethanol solutions and propanol solutions have large difference with that of water. The experimental results show that, the mean error of glucose solutions and NaCl solutions by the linear model is 2.9447×10-4, the mean error of the tested solutions by the refractive index calculation model with surface tension modification is 1.4381×10-4, and the maximal relative error of tested solutions is 0.1258%. The proposed method is meaningful to extend applicability of fiber-capacitance droplet analyzers and improve the accuracy of refractive index measurement.