The invention discloses a tung oil-based polyol preparation method, which comprises: mixing tung oil, a biocatalyst and a hydroxylating reagent according to a certain ratio, and heating to a temperature of 40-60 DEG C under stirring; slowly adding a hydrogen peroxide solution in a dropwise manner under a rapid stirring condition, and carrying out a constant temperature reaction for 6-15 h after completing the adding; filtering and separating the biocatalyst after completing the reaction; and neutralizing the reaction system, carrying out water washing, and carrying out pressure reducing distillation to obtain the tung oil-based polyol. According to the present invention, the conjugated double bond of tung oil can improve the reactivity of the epoxy group, such that the oil-soluble fatty acid is added while the epoxidation is performed so as to make the reaction system use the biocatalyst to perform catalytic conversion, effectively avoid the occurrence of the cross-linking side reaction and efficiently synthesize the tung oil-based polyol product; and the prepared tung oil-based polyol has the hydroxyl value of 120-270 mgKOH/g, the acid value of less than 1.0 mgKOH/g, the moisture content of less than 0.1 wt% and the yield of more than 92%, and is suitable for the preparation of polyurethane materials.