The fiber Fabry-Perot interferometer used to measure the refractive index modulation of polymer-dis-persed liquid crystal is introduced. From measuring the quantity of the interference fringe shift with a CCD based on the theory of isoclinal interference fringes formatting, the maximal refractive index modulation versus different external voltages, 3. 899× 10-3 in the extemal voltage of 57.4 V/μm, and the dynamic refractive in-dex modulation versus response time in the extemal voltage of 8 V/μm are found in our prepared 1. 250 mm-thick PMMA/E49/TNF/ECZ polymer-dispersed liquid crystals. The experimental results will be helpful to un-derstand the photoinduced reaction mechanism of the material and optimize the mixture ratio of each component.