In standard fiber transmission systems ,imperfections in the core-cladding interface introduce random birefringence th at leads to light being randomly polarized.These problems with random birefringe nce in polarization maintaining (PM) fibers are overcome by deliberately introdu cing a larger uniform birefringence throughout the fiber.Current PM fibers realized by standard fiber technology include PNDA or bow-tie fibers,which ach ieve this goal by applying stress on the core region of a standard fiber.A modal birefringence up to 5×10－4 may be readily obtained.However, this kind of fibers is so sensitive to the change of environment that the stabil ity of systems can be seriously affected.In the other hand,PM photonic crystal fibers (PCFs) with asymmetric core designs,wh ich offer resistance to the change of environment,may be used to introduce modal birefringence at least one o rder of magnitude larger than that for conventional PM fibers.This paper studies the relationship between the arrangin g shape and size parameters of air holes in total internal reflection (TIR) PCF and the b irefringence.A kind of single-mode two-hole center-defected PCF with a birefringence of 3.4×10－3 is des igned th rough structure optimization. Meanwhile,numerical empirical equation for this kind of PCF is achieved by the method of multi-variant nonlinear regress fitting,which may offer theoretical reference for the manufac ture of PM-PCF in future.