We study and analyze the propagation and the characteristics of light in structure, and find that by increasing the sizes of air holes in the two rows that are adjacent to the middle slab, there appears only one polarization state that can propagate in the waveguide within the complete photonic band gap at a specific frequency. Then we propose a new structure of polarization beam splitter based on the principle. The results of calculation and simulation show that the device can separate TE mode from TM mode effectively with a large angle. And the device size is less than 17.6μm×9.8μm.We believes that it will have potential applications in the photonic integrated circuits.