We propose an electrooptic photonic crystal with a periodically poled lithium niobate (PPLN) waveguide structure based on electrooptic effect, where the group velocity of input optical beam can be continuously modulated from subluminal to superluminal by adjusting the applied external electric field in the z-direction of the crystal. The slow light propagation at the band edges was investigated and analyzed, in which a large group index in a PPLN waveguide was obtained, and the group refractive index or the transmission as a function of the applied electric field, operation temperature, and different input wavelength were also presented and discussed in detail.