A method for chirped fiber Bragg grating (FBG) fabrication using an uniform phase mask is proposed. In the scanning exposure process, the phase mask jitters periodically along the length direction, and the jittering amplitude varies with the grating scanning length, which causes the phase of FBG changing with the position of the mask. As a result, the period of FBG is modulated linearly, and a linely chirped FBG is obtained. The chirped coefficient of FBG is determined by the variation of the jittering amplitude of phase mask. Three different jittering functions of phase mask are designed, and FBGs with different chirp values are fabricated in experiment.