Abstract: According to the cure molding process of polymer matrix composite, an optical fiber sensor system was established for testing the pressure change in the normal direction of prepreg layers, and the applicability of this system was also evaluated. As a result of experimentation, this sort of optical fiber sensor can be used in the environment where the measuring temperature is under 120℃ and measuring pressure between 0.005~0.5 MPa, steadily and repeatedly. The effect of flex density, the measuring temperature and micro bend rebound of the fiber optical sensor during the mould forming process are given. The fit equation is performed with varying loading and a comparison of numerical results with known experimental data confirms the approximate validity of the fit equation.