Based on the transfer matrix method, a detailed theoretical and numerical study on double-phase-shifted fiber Bragg grating (FBG) is investigated. Temporal responses of the double-phase-shifted FBG to optical pulse are analyzed and the influence of the two phase-shifts’ position on the reflected output pulse is evaluated. Results demonstrate that very different temporal pulse waveforms can be achieved by adjusting the length ratio (α=L₂/L₁). Specifically, a transform- limited Gaussian input optical pulse can be shaped into flat-top square pulse (α=1.81) or two identical optical pulse sequences (α=1.93).