A holey fiber with beat length independent of wavelength is designed by combination of two defect structures respectively with positive and negative birefringence. The radius of a pair of air holes adjacent to the core is enlarged and the other circular air holes in the cladding are substituted with elliptical holes at the same time. Birefringence with different signs generated by these two changes may interact with each other so that the beat length is less sensitive with wavelength. Finite-difference beam propagation method (FD-BPM) is used to calculate and analyze the influence of different structural parameters on birefringence of holey fiber. Stable beat length can be achieved at some wavelength window by adjusting the structural parameters and the value of the beat length can also be tuned according to practical requirement. Uniform beat length with more than 180 nm bandwidth at 1310 nm wavelength window is obtained by optimizing structural parameters of holey fiber.