Three asymmetric structures are introduced into cross-section of holey fiber by changing the size of diameters of micro holes near the fiber core while maintaining the hexagonal lattice. The linear variation of birefringence over wavelength is controlled and expanded by the compensation between the positive and negative ones. Full-wave beam-propagation-method is used to calculate influence of different structural parameters on the beat-length dispersion, including the material dispersion of fused silica. Considering the permission of fabrication art, flat dispersion curve of beat-length about 9 cm is obtained by parameters′ optimization in super-wide band covering both 1310 nm and 1550 nm wavelength windows commonly used in the optical telecommunications. The relative change of beat-length is less than 0.15% in 1250~1650 nm band, and 0.85% in 1000~1900 nm. This optimal fiber is suitable for making wideband fiber-optic wave-plate used in fiber sensors to promote the systematic stability and liability.