Abstract: he fiber Bragg gratings (FBG) have found wide applications in the field of communication and sensing. Temperature, strain and other physical parameters can be measured by detecting the shift of the central wavelength in FBGs, but cross sensitivity of FBG to temperature and strain needs to be solved. The principle and advantage of FBG sensors are investigated briefly, reference grating method and Erbiumdoped fiber amplifying method to separate the temperature effect are given. A method to demodulate the shift of the central wavelength in FBGs by using the main mode and the side mode of a tilted fiber grating is introduced. With this method, the effect of temperature on strain detection is discriminated successfully.