The present invention discloses a 3D polarization beam splitter based on 2D photonic crystal slabs which comprises a 2D photonic crystal slab positioned at the top part, a 2D photonic crystal slab positioned at the bottom part and perpendicular to the top 2D photonic crystal slab, and an input coupling dielectric block; a P polarization wave output waveguide is positioned in the top 2D photonic crystal slab; an S polarization wave output waveguide is positioned in the bottom 2D photonic crystal slab; the output port of the P polarization wave output waveguide and the output port of the S polarization wave output waveguide are apart from each other in 3D space; the photonic crystal slabs include a background dielectric material and dielectric rods. The structure of the present invention has a small volume, high degree of polarization, high light transmission efficiency; it is convenient for optical integration and highly efficient; it is suitable for large-scale optical integrated circuits; and it can realize the polarization beam splitting function for different wavelengths.