Polydimethylsiloxane (PDMS) is a polymer organic silicon compound, which is widely used in microfluidic chip preparation, biology, optics, and composite material matrix. The optical fiber interferometer is constructed through the combination of PDMS and optical fiber structure, the refractive index and linear expansion pressure response characteristics of PDMS are tested by optical fiber sensing technology. Experimental results show that the rate of change for refractive index of PDMS with the pressure is -2.1×10^-2 RIU/MPa (RIU is the unit of refractive index), the rate of change for linear expansion of PDMS with the pressure is 17.3 μm/MPa. The refractive index and linear expansion pressure response of PDMS are studied in the form of optical measurement, which has higher accuracy and reliability.