The structure and principle of a novel sensor with in-fibre Bragg grating (FBG) and extrinsic Fabry-Perot interferometer (EFPI) in series, used for simultaneous strain and temperature measurement, are presented. The cross-talk between the reflective spectra of the FBG and the EFPI interference spectra is observed which has been reduced by the method of averaging the wavelengths at the two points of 3 dB bandwidth to improve the accuracy for temperature measurement. This sensor has been applied to simultaneous strain and temperature measurement for 3-D braided composite materials. The experimental results show that this method has a strain accuracy of ±20 με and a temperature accuracy of 1 ℃, which can meet the requirements for practical applications.