Birefringence of asymmetric photonic crystal fiber is investigated using the finite element method, under the
circumstance of perturbation. By comparing the value of birefringence on the different value of large air-hole, the results
indicate that when the intrinsic-birefringence is smaller, the random offset of hole-position has large influence on the
birefringence. With the intrinsic-birefringence increasing, the little effect on birefringence regardless of the offset of
hole-position or the variation of hole-diameter.