A way is proposed to modulate light propagation in one dimension photonic crystal with acoustic wave. The transfer matrix method is induced to calculate the reflective spectrum and acousto-optic interaction in a fiber Bragg grating (FBG). It is approved that sideband wavelength and reflectivity can be fine adjusted by changing the acoustic wave. The result shows a 30 ps group delay is achieved on a 10 cm FBG. This method can be applied to novel devices of photonic crystal such as tunable filters.