The invention discloses a preparation method for hydroxaminopolyether. The preparation method comprises the steps of adding polyether polyol, a catalyst, a co-catalyst and epoxy chloropropane into a sealed high-pressure reaction kettle according to a ratio, wherein an end group is a chloro-substituted polyether intermediate; and adding a reaction solvent and an amination reagent into the filtered chloro-substituted polyether intermediate, and reacting to prepare a pure hydroxaminopolyether product. According to the preparation method, Lewis acid serves as the co-catalyst for the first time and is applied to a ring-opening polymerization reaction of DMC catalyzed polyether polyol and epoxy chloropropane, so that the shortcomings of low catalyst efficiency, high reaction pressure, strict device requirements and a large amount of byproducts in a conventional method are overcome and the efficient synthesis of chloro-substituted polyether is realized; and in addition, hydroxaminopolyether synthesized by taking sodium amide as the amination reagent has relatively high conversion rate and high amine value.