The invention discloses a high temperature-resistant leakage stopping agent, and a preparation method and an application thereof, and belongs to the technical field of petroleum drilling leakage stopping. The high temperature-resistant leakage stopping agent comprises, by mass, 2-3% of polyacrylamide, 1-2% of sulfonated phenolic resin, 0.9-2% of hexamethylenetetramine, 3-5% of a water swelling type granular plugging agent, 2-6% of a unidirectional pressure blocking agent, 0-3% of an alkaline pH regulator, and the balance of water. The leakage stopping agent has good high temperature resistance, and can meet leakage stopping needs of 80-150 DEG C drilling. The leakage stopping agent has low viscosity and low fluidity before forming gel, and is convenient for leakage stopping construction; and the leakage stopping agent has high strength and high stability after forming the gel, and has good plugging performance.