In this paper, we propose a new type of a polarization switch bases on KDP waveguide structure. The Czychroski’s method applied in de-ion water solution is introduced. We also show the experimental result of crystal growth by this method. The design principle of the TIR type switch is discussed to find the relationship between applied voltage (the electric field) and reduction of the refraction in a y-cut and x-propagation KDP substrate. We compare the insertion loss of KDP and other kinds of substrates to show the advantage of KDP crystal.