The invention discloses a method for separating tin from waste tinplate and preparing tin dioxide. The method comprises the following steps: (1) grinding waste tinplate, screening; (2) washing the screen underflow with soda water; (3) filtering the washed material, leaching filter residue with sodium hydroxide solution and oxidant, filtering the leachate, wherein the filtrate is sodium stannate solution; and (4) introducing carbon dioxide in the sodium stannate solution, filtering, and washing to obtain the tin dioxide product. The preparation method of the invention has low cost and pollution and remarkable economic value and market competition.