The invention relates to a high-temperature leveling agent, and a preparation method and an application thereof. The high-temperature leveling agent is prepared from 0.1-1% of a polyester-polyether-silicon oil block copolymer, 9-10% of polyethylene glycol monostearate, and balance of water. The polyester-polyether-silicon oil block copolymer is prepared from the raw materials of, by weight: 120-160 parts of polyethylene glycol, 18-30 parts of glycol, 15-25 parts of dihydroxy polyether, 20-28 parts of dimethyl terephthalate, 10-30 parts of an amino-terminated double-head sealant organosilicon, 5-10 parts of 3-piperazine propyl dimethoxysilane, and 0.2-2 parts of metal acetate. With the high-temperature leveling agent provided by the invention, dyeing quality of polyester fiber or fabric thereof can be improved, and the dyed polyester fiber or fabric thereof is provided with excellent fluffy and soft property, good antistatic performance, and good hydrophilic property. The dyed polyester or fiber thereof can be provided with excellent comfortableness with no other finishing.