The invention relates to a method for preparing a polyvinyl alcohol/polyether sulfone (PVA/PES) pervaporation composite membrane. The method comprises the following steps: placing and soaking PES in 0.05 to 5 weight percent borax aqueous solution for 6 to 12 hours; dissolving PVA dissolved in deionized water at a temperature of between 80 and 95 DEG C to prepare casting solution of which the mass concentration of the PVA is 1 to 7 weight percent; cooling the casting solution to between 20 and 25 DEG C; placing the treated PES in the PVA casting solution; preparing a PVA separation layer with the thickness of 1 to 8 microns on PES base membrane and then drying at a temperature of between 20 and 25 DEG C so as to obtain composite membrane; and placing the obtained composite membrane in acetone solution containing glutaraldehyde accounting for 5 to 20 volume percent of the total volume and HCl accounting for 0.1 to 0.15 volume percent of the total volume and treating for 0.5 to 5 hours at a temperature of between 20 and 50 DEG C. The preparation method has the advantages of simple process and easily controlled condition. The membrane is applicable to the separation of water/glycol mixture, and the permeation flux of the composite membrane can be up to 445 g/(m<2>h).