A broad-band optical fiber coupler with asymmetric dual-core photonic crystal fiber is proposed based on theoretic analysis. Analysis of numerical simulation shows that coupling ratio of the coupler is flattened in a wider range of wavelength. The influence of the size of air hole between the two the core of the coupler and the polarization of propagating light on the characteristic of coupling by using the finite element method is simulated and analyzed. The results show that the optical fiber coupler with asymmetric dual-core photonic crystal fibers has a 50% coupling ratio with a ±4% dependence on the wavelength over 1.3 μm-1.8 μm,so it is suitable for optical fiber communications and other fields of broad-band couplers with the demand.