The invention provides a synthetic method for trifunctional and high-cohesive-energy flame-retardant polyol used for a woodworking adhesive. The synthetic method comprises the following steps: step 1,accurately weighing adipic acid, hexanediol, tris(2-hydroxyethyl)isocyanurate, a catalyst and an antioxidant, and carrying out a reaction at 140 DEG C for 1 h under the protection of nitrogen; step 2, carrying out heating to 150 DEG C, carrying out a reaction for 1 h, carrying out heating again to 167 DEG C, carrying out a reaction for 1 h, then carrying out heating again to 184 DEG C, carrying out a reaction for 1 h, carrying out heating again to 201 DEG C, carrying out a reaction for 1 h, carrying out heating again to 218 DEG C, and carrying out a reaction for 2 h; and step 3, opening a vacuum pump connected with a reaction device, raising a vacuum degree to less than minus 0.096 MPa in 2 h, periodically carrying out sampling for detection until an acid value and a hydroxyl value of a sample meet standards, then carrying out cooling to 180 DEG C, breaking vacuum with nitrogen, carrying out cooling to 160 DEG C, and carrying out discharging and packaging so as to obtain a product. According to the invention, through introduction of the tris(2-hydroxyethyl)isocyanurate, the cohesive energy, crystallinity and wettability of a polyurethane adhesive are improved; and when the trifunctional and high-cohesive-energy flame-retardant polyol is applied to the woodworking adhesive, the initial adhesion of the polyurethane adhesive can be well improved.