Based on the transfer matrix method,the reflective spectrum characteristics of the phase-shifted fiber grating are analyzed by detailed theoretic. The corresponding mathematical model is established and validated. It is shown that the phase shift leads to the split of the reflective spectrum of the fiber grating. The wavelength of the split point is linearly and periodical to the phase shift. The reflectivity of the split point is symmetrical to the phase-shifted position and the central wavelength of the fiber grating. And the reflectivity of split point is approximately hyperbolically tangential versus the phase-shifted position.