Based on multi-pole method theory, a kind of hybrid cladding photonic crystal fiber（PCF） is designed. It has been shown theoretically that it is possible to obtain fiattened dispersion charactor of dispersion absolute value 125 ps·km-1·nm-1 within the wave band of 144 μm to 20 μm by altering four structure parameters of the five-ring hybrid cladding in the PCF (namely the diameter of the inner ring hole, the diameter of the outer four ring holes, the pitch of the hexagon and the pitch of the octagon). Moreover, value simulation results show that in the PCF low confinement loss of 0005 dB/km in the 144—20 μm wavelength range can be achieved.