When a fiber Bragg grating is subject to an uneven strain, both of the fiber core index and the grating pitch will experience an uneven variation and therefore the resonant wavelength will vary along the grating. The interaction model between fiber Bragg grating and uneven strain field is established, and the relationship of the fiber Bragg grating reflective spectrum response to the uneven strain is deduced. The results of interaction experiments between linear distribution strain field and fiber Bragg grating are given.