The invention discloses a cationic surfactant prepared from waste polyester, and a preparation method thereof. According to the preparation method, a mixed catalyst is adopted to realize high efficiency alcoholysis of waste polyester, halogenation reaction is adopted, and the novel cationic surfactant with high activity and high bactericidal activity is prepared via reaction of waste polyester with alkyl morpholine. The preparation method comprises following steps: waste polyester alcoholysis, preparation of a halogenation intermediate, and preparation of the cationic surfactant, wherein BHEXand a long-chain alkyl morpholine (RNA) at a molar ratio of 1:2-1:2.5 are introduced into a reactor containing excess acetone, are heated to 50 to 57 DEG C for 1 to 5h of reaction, an obtained productis subjected to underpressure distillation at 25 to 30 DEG C to remove acetone so as to obtain a finished product. The cationic surfactant is stable in product performance, high in yield, is convenient for industrialized production, is capable of realizing effective recovery and recycling of waste polyester fiber, and is high in application value.