To meet the demand for curvature measurements in the fields of intelligent biomedical equipment and soft robotics, among others, a flexible curvature sensor based on a polyvinyl chloride (PVC) and silicone composite substrate was proposed and has been designed. Firstly, a fiber Bragg grating (FBG) sensor was embedded into a silicone film, which was pasted onto the surface of a PVC substrate. Then, calibration experiments were carried out to evaluate the reflection spectrum and wavelength shift of the sensor. Finally, the sensitivity and repeatability of the sensor based on the composite and silicone substrates were tested experimentally. The experimental results show that the sensitivity and repeatability of the FBG curvature sensor can be improved by using a PVC-reinforced substrate. The maximum sensitivity of the FBG sensor with the composite substrate is 245.5 pm/m-1 and its deviation index is less than 3%. The sensor has wide application prospects in the fields of soft robotics and biomedical curvature measurements.