We investigate the dispersive property of a A-type atomic system embedded in photonic band gap structures.The atomic coherence is established by the structured reservoir which consists of a double-band photonic band gap (PBG) and defect modes. With an atomic density of 7 × 1015 atoms/cm3, the group velocity of a probe laser being detuned far away from the gap is shown to be reduced to 3 × 102 m/s near the transparency window associated with the PBG edges and 6 × 103 m/s at the transparency window associated with the defect modes, without using any deriving field. The influence of the smoothness of the density of modes and the decay rate of the second ground state of atoms are analysed.