Abstract: In order to study the photonic band gap and dispersion property of a dual-core photonic crystal fiber(PCF),the photonic band gap was calculated with the plane-wave expansion method.The calculation results show that when the relative aperture(d/Λ)is larger than 0.2,the normalized propagation constant(β/Λ)increases,so the prohibited band and the range of wavelength propagating in the air-core increase.Secondly,the dispersion property of a dual-core was analyzed with a full vector model.The results show that the dispersion property can be adjusted with different structure parameters of fibers.Results show about 480nm of super flat dispersion area near 1.55μm can be obtained with Λ=2μm,d/Λ=0.4; with the relative aperture and aperture distance increasing,zero dispersion point will move to shorter-wave.The results of this study provide an effective way to produce efficient transmission optical fibers and high-performance polarization fibers.