A broad-spectrum unclad fiber-optic chemical sensor based on the sample refractive index is fabricated, which integrate an improved approach of measurement that is called mode-filtered light detection. A good result has been obtained by applying this sensor to the detection of ethylene glycol. It shows that this sensor has good stability and reproducibility by measurement of two samples with different concentrations with relative errors of 0.31 % and 3.33%, respectively, and detection limit of 2% (v/v).