The influence of cladding air holes and filling rate on the dispersion characteristics of photonic crystal fiber is studied. The results show that the dispersion characteristics of photonic crystal fiber can be changed flexibly by adjusting package layer hole pitch and air holes. Based on this situation，relatively flat dispersion curve can be designed near a given wavelength at 1550nm. The finite element method was used to simulate the optical field distribution of transmission in the photonic crystal fiber，which is of great significance in the long and large capacity optical communication system.