The invention discloses a preparation method of high-performance forward osmosis membrane and relates to a method of membrane modification. The preparation method aims at solving the problem that the salt back-mixing flux of existing sea water desalination forward osmosis membrane is high. The method comprises the following steps: 1, mixing a membrane forming polymer, an addition agent and a solvent to prepare membrane casting liquid, and forming membrane by a phase inversion method; 2, putting the membrane in hot water bath to dip, then putting the membrane in an organic solution to dip, using deionized water to wash, putting the membrane in glycerol aqueous solution to dip, after taking the membrane out, drying the membrane by airing, storing the membrane in a drying tank. According to the preparation method of the high-performance forward osmosis membrane, common chemical reagents are used for preparing a macromolecule permeable membrane material, so that under the condition of keeping water flux not to be reduced (even if the water flux is increased), the salt back-mixing flux is lowered, the selectivity of forward osmosis technology to ions (or molecules) in water is effectively improved, and the preparation method has very important practical significance to the practical application of the forward osmosis technology. Meanwhile, the preparation method has advantages of being simple in process, convenient to operate, low in reagent price and high in repeating utilization rate.