The present invention discloses a TEOS with a high extinction ratio based on slab PhCs which comprises an upper slab PhC and a lower slab PhC connected as a whole; the upper slab PhC is a first square-lattice slab PhC, the unit cell of the first square-lattice slab PhC includes a high-refractive-index rotating-square pillar, three first flat dielectric pillars and a background dielectric, the first flat dielectric pillars include a high-refractive-index dielectric pipe and a low-refractive-index dielectric, or 1 to 3 high-refractive-index flat films, or a low-refractive-index dielectric; the lower slab PhC is a second square-lattice slab PhC with a complete bandgap, the unit cell of the second square-lattice slab PhC includes a high-refractive-index rotating-square pillar, three second flat dielectric pillars and a background dielectric is a low-refractive-index dielectric; and an normalized operating frequency of the TEOS is 0.4057 to 0.406.