The invention discloses a terylene deweighting dyeing assistant, and a preparation method and a use thereof. A raw material formula of the terylene deweighting dyeing assistant comprises, by mass, 10-15% of ethylene glycol monobutyl ether, 10-15% of 1,4-butanolide, 10-20% of fatty alcohol polyoxyethylene ether, 10-20% of secondary alkane sulphonate, and the balance water, wherein the molecular formula of the fatty alcohol polyoxyethylene ether is RO-(CH2CH2O)n-H, n is 7-9 or 15-20, and R is a C12-18 alkyl group; and the molecular formula of the secondary alkane sulphonate is R'SO3Na, and R' is a C10-13 alkyl group. The terylene deweighting dyeing assistant guarantees the terylene dyeing effect and the silk like effect and adopts a one-bath technology; and compared with traditional technologies, the technology has the advantages of saving of a lot of time, energy and substances, and great reduction of the pollutant emission.