The invention discloses a high-performance flat plate type cellulose acetate / nano-titanium dioxide blended forward osmosis membrane, which is prepared by comprising the following steps: adding the following raw materials in percentage by weight: 7.0%-26.0% of cellulose acetate, 2.0%-16.0% of additives, 0.1%-5.0% of nano-titanium dioxide, 0.05%-0.1% of graphene, and a dimethylformamide or dimethylacetamide, N-methylpyrrolidine and acetone mixed solvent into a dissolving tank according to certain sequence, stirring and dissolving for 3-15h to be full and even at 25-90DEG C, thus obtaining blended forward osmosis membrane casting liquid; and preparing the high-performance flat plate type cellulose acetate / nano-titanium dioxide blended forward osmosis membrane on a supporting material by using a phase conversion method. According to the prepared forward osmosis membrane, 1M NaCl and deionized water are respectively taken as driving liquid and feed solution, the flux of pure water can reach more than 17.5L / m<2>.h during testing time of1h and the backward salt flux is less than 3.0g / m<2>.h.