A photonic crystal polarizing beam splitter based on directional coupling structure is proposed. The beam splitter consists of two single-mode waveguides. By adjusting the width of the two single-mode waveguides, the coupling length can be changed. The splitter is simulated and analyzed by using finite-difference time-domain method. The results show that at the wavelength of 1550 nm, both TE and TM polarizations achieve mode split. The transmissivities of TE and TM modes both exceed 90% and the extinction ratios reach 22.4 dB and 18.2 dB respectively. The size of the device is only 25.8 μm×13 μm.