Due to different strain of different components along the grating axis when Bragg grating is employed to measure strain(statically,dynamically),central FBG wavelength shift changes accordingly. However effect of this strain difference on central wavelength shift of fiber Bragg grating is often ignored in practical application. With coupled mode theory,as well as grating segment and transfer matrix method,chirp characterizations of fiber Bragg grating are studied when axial linear and high-order strain,non-linear periodic strain-wave are applied. Based on different chirp characterizations,measurement condition and measurement range under various kinds of strain are determined.