A modified photonic quasicrystal fiber is designed which has an octagon-fold symmetric quasicrystal array of air holes in the cladding. Small air-holes of the inner two rings and large air-holes of the outer rings in the cladding are adopted. The dispersion properties are analyzed by using the full vector finite-difference frequency-domain (FDFD) method with anisotropic perfect match layer (APML) absorbing boundaries. Its dispersion curve is calculated, when the distance between adjacent air holes is from 1.40 μm to 2.50 μm, the small air-hole diameter is from 0.10 μm to 0.50 μm and the large air-hole diameter is from 0.20 μm to 1.00 μm.The results show that the flattened dispersion at different levels can be obtained by adjusting the diameters of two kinds of air holes and the distance between adjacent holes in the cladding.