The new phase grating based on two-dimensional structured thin films is reported. The rigorous coupled-wave analysis (RCWA) is employed to calculate the diffraction efficiency which varies with incident wavelength and angle. According to the result obtained by using RCWA, when the wavelength ranges from 600 to 640 nm, TE mode and TM mode can be diffracted in the transmitted 0th and ±1st orders, respectively, at normal incident angle. For example, at the wavelength of 633 nm, the polarization extinction ratio of 0th order is I0,TE/I0,TM=109.8, and the polarization extinction ratio of ±1st order is I±1,TM/I±1,TE =334.6. This polarizing beam splitting phenomenon is confirmed by theoretical simulation with finite-difference time-domain method, which shows that TE mode and TM mode can be separated by an angle of about 10°in glass substrate. The same simulation method is performed for the diffraction at incident angle of 23° in order to compare with the results from RCWA and grating equation calculation.