A new type of microstructured optical fiber with a high birefringence tunable effect is designed by introducing two large air holes in a core region to induce local birefringence and reducing the hole lattices in the x-direction to induce global birefringence. Polarization properties and modal field characteristics of this fiber based on polymethyl methacrylate materials are investigated by using the full vectorial plane wave method. The results show that the fundamental mode birefringence has two maxima in an optical communication wavelength band, and the magnitude and position of the maximum birefringence can be adjusted by changing the wavelength and the structure parameter of this fiber. By adjusting the air holes diameter and hole lattices in the x-direction , the simulation results show the optimized design parameters of this fiber with high birefringence and zero polarization mode dispersion.