The invention relates to a preparation method for a dried reverse osmosis composite membrane. The preparation method comprises the following steps: soaking a conventional reverse osmosis composite membrane in a protector-containing aqueous solution, wherein the soaking temperature is 10-50 DEG C and the soaking time is 1-10 minutes; and then carrying out thermal treatment for 8-12 minutes in an oven at 80-100 DEG C, wherein the protector is one or a mixture of more of sodium hydrogen sulfite, potassium hydrogen sulfite, ammonium hydrogen sulfite, formic acid, oxalic acid, citric acid, dipotassium glycyrrhizate, butylated hydroxyanisole, butylated hydroxytoluene, propylgallate, tert-butylhydroquinone, tea polyphenol, 3,4,5,7-tetrahydroxy flavone and a glycyrrhisoflavone solution. The preparation method provided by the invention not only can be used for realizing dry state storage of the reverse osmosis composite membrane, but also can effectively solve the problem that the dried reverse osmosis composite membrane is attenuated in performance in a long-term storage process.