To fabricate the Sagnac interferometer sensor, a polarization-maintaining fiber with the length of 8 cm was spliced between two single-mode fibers, and the polydimethylsiloxane material was coated on the polarization-maintaining fiber, then the polydimethylsiloxane functionalized polarization-maintaining fiber was integrated into a fiber coupler to form a Sagnac loop. When the polydimethylsiloxane absorbs volatile organic compounds, the polydimethylsiloxane will be swelled and the wavelength of interference peak will shift, so that the concentration of volatile organic compounds can be measured by monitoring wavelength shift. The response of the sensor to the concentration of volatile organic compounds was measured experimentally, and the results show that the sensitivity of the sensor is 1.03 pm/ppm when the concentration ranges from 0 ppm to 6 000 ppm. The optical spectrum analyzer with a 0.02 nm measurement precision was used in experiments, so the precision could reach about 19.4 nm in the concentration range from 0 to 6 000 ppm. The sensor′s sensitivity improves 4 300 times which compared to grating fiber with polydimethylsiloxane material sensor.