The grapefruit photonic crystal fiber is simulated using finite element method (FEM). The effective refractive index and field distribution of each mode are calculated. Based on the coupled mode theory and correlation function mode-solver, the transmission spectrum of fiber Bragg gratings in grapefruit photonic crystal fibers is studied and the result explains the reason of multiple peaks. The influence of the structure change of the fiber core diameter and air hole size on the transmission spectrum is simulated. The results show that the resonance wavelength would shift to the longer wavelength with the increase of the diameter of the fiber core. The resonance wavelength would shift to the shorter wavelength with the increase of the size of the air holes, and the change is different for each resonant pattern. The fabrication of Bragg grating in a photonic crystal fiber is investigated experimentally by phase mask method. Experimental data are consistent with simulation numerical results.