The invention relates to a high-temperature-resistant slow-expansion water-absorbing expansion resin plugging aid used in the field of oilfield drilling. The preparation method comprises: putting water into a reaction tank, adding bentonite, completely dispersing, sequentially adding acrylamide, acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid, completely dissolving, introducing nitrogenat a low temperature, sequentially adding a cross-linking agent and an initiator, heating to 30-70 DEG C, reacting for 2-5 h, drying, granulating, and screening; and adding a wrapping agent and a solvent into the reactor, slowly heating, adding a water-swelling resin after the wrapping agent is completely dissolved, and removing the solvent after the reaction is finished so as to obtain the high-temperature-resistant slow-expansion water-absorbing expansion resin. According to the invention, the obtained product can slowly expand in the early stage of water absorption, can rapidly achieve water absorption expansion within a short time in the later stage, has a delay time of longer than 1 h, has temperature resistance of 140 DEG C, can effectively plug at a high temperature, and can achieve good repairing effect.