The invention discloses a preparation method of titanium dioxide composite sizing agent used by dye sensitized solar cells, comprising the following steps: 1) after mixing titanyl sulphate and water, standing; 2) filtering, carrying out hydro-thermal treatment in a hydrothermal agitated reactor, washing until no sulphate radicals remains, and obtaining a product A with fixed moisture content; 3) putting milky suspension obtained after mixing the product A with NaOH into the hydrothermal kettle, heating, dipping the product by HCl after reaction ends, carrying out centrifugal separation, washing and obtaining a product B; and 4) mixing the product A with the product B, mixing with an organic carrier, carrying out rotary evaporation or distillation, and obtaining the titanium dioxide composite sizing agent used by dye sensitized solar cells, which is suitable for large-area screen print. The method has low preparation cost and simple preparation technology, and prepared batteries have good performance.