Based on the transfer matrix method and the couplemode theory, the characteristics of reflective spectrum and phase shift of the phaseshifted fiber Bragg gratings were analyzed. The result showed that the transmission windows in the reflection spectrum increased and the phase jumped frequently with the increasing of the phase points, thus the differential effects on signals were generated. Besides, the phase differential orders were proportional to phaseshift points. On this basis, a pulse shaper was designed based on the characteristics of the differential phase shift grating. By optimizing the weighting factors for each order derivative of the Gaussian input pulse, the output pulse can be formed the shapes of rectangular and triangular. By changing the length ratio of the first section optical fiber grating and the second section, the distorting phenomenon of the triangular output pulse was improved. Finally, changing the Gaussian input pulse width by ±5%，the output waveform were synthesized as rectangular pulse and triangular pulse. Thus the stability and practicality of the pulse shaping system were verified.