All-solid photonic bandgap fibers have being used for supercontinuum generation. The spectral rang of supercontinuum is controllable with the use of bandgap. But the dispersion has significant effect on supercontinuum generation. In different bandgaps of the same photonic bandgap fiber and in the same order bandgaps of different photonic bandgap fibers, the group velocity dispersions were calculated with plane-wave methods. The results indicate that the relative position of the zero dispersion wavelength in the bandgap strongly depends on the location of the corresponding bandgap. Zero dispersion wavelength is in the proximity of the short wavelength edge of bandgap in long wavelength region.However, it is located near the long wavelength edge of bandgap in short wavelength region. From the calculated waveguide dispersion and material dispersion, it can be found that it is material dispersion that affects the relative position of zero dispersion wavelength in bandgap.