The invention relates to polyester resin for low-temperature cured powder paint and a preparation method of the polyester resin. The polyester resin is characterized by comprising the following ingredients in percentage by mass: 0 to 10 percent of ethylene glycol, 10 to 40 percent of neopentyl glycol, 0 to 8 percent of 1,6-ethylene glycol, 0 to 5 percent of 1,4-cyclohexanedimethanol, 20 to 60 percent of terephthalic acids, 2 to 15 percent of adipic acid, 0.05 to 0.2 percent of monobutyltin oxide, 0.02 to 0.15 percent of triphenyl phosphate, 0 to 5 percent of adipic acid, 2 to 40 percent of m-phthalic acid and 0 to 5 percent of methacrylic acid. The polyester resin and the preparation method have the advantages that the curing at the low temperature condition of 130 DEG C to 140 DEG C can be realized, in addition, the storage stability is good, and the like.