A novel type of photonic bandgap fiber (PBG-PCF) applied to pulse and slow light is proposed. The designed PBG-PCF is composed of a hollow core and seven cladding layers with air hole arranged by triangular lattice. Its band structure, group index and group velocity dispersion are analyzed in detail by using plane wave expansion method. The simulation results show that slow light property can be improved effectively by microfluid infiltration for the air holes of the inner cladding of PBG-PCF, and an ultra-wide-band photonic crystal slow light optical fiber with a group index of 6, a wide band more than 100 nm, which can transmit flat slow light, is realized. The designed PBG-PCF has promising and potential applications in communication networks, signal processing, optical sensors and nonlinear interactions.