In this paper,a polarization independent beam splitter basedon silicon based wav eguide is proposed.The deice consists of a symmetric directional coupling struct ure and a sub-wavelength structure.Accordoing to the coupled mode theory,the co upling strength of the TM mode is stronger than the coupling strength of the TE mode in a traditional directional coupling structure,and it is difficult to achi eve polarization independent beam splitting.By using the subwavelength structure in the coupling region,the coupling strength is enhanced for TE mode and is wea kened for TM mode,so that the coupling strength could be equivalent between TE a nd TM modes.Therefore,polarization independent beam splitting can be achieved by adjusting the parameters of the directional coupling structue and the sub-wave length structure.The time domain finite difference method (FDTD) is used for sim ulation analysis.The results show that the device can achieve polarization indep endent beam splitting at 1550nm.The excess loss of the TE mo de is 0.27dB,and the excess loss of the TM mode is 0.55dB.The coupling region length of the device is 5.48μm,and the bandwidth is about 25nm.The device h as the advantages of small size,simple structure and easy integration.