The invention discloses a method for preparing ultra-low molecular weight hyaluronic acid oligosaccharides and a salt thereof through combination of solid-liquid biphasic enzymolysis and ultrafiltration. The method comprises the following steps: degrading hyaluronic acid and a salt thereof by utilizing hyaluronidase produced by bacilli; preparing high-concentration hyaluronic acid enzymatic hydrolysate by adopting the method of combining a solid-liquid biphasic enzymolysis system and an ultrafiltration system, and then performing inactivating, activated carbon adsorption and impurity removal,filtering and spray-drying to obtain the ultra-low molecular weight hyaluronic acid oligosaccharides and the salt thereof with the molecular weight of less than or equal to 3 kDa. The product preparedby the method is high in stability, ultra-low in molecular weight, good in inflammation resistance and percutaneous absorptivity, high in purity, strong in oxidation resistance, does not have cytotoxicity, has the advantages of repairing skin cell damage and the like, and can be widely applied to the fields of cosmetics, food and medicines. According to the method, the process flow is easy to operate; conditions are mild; various alcohols are not used; the energy consumption is relatively low; the method does not have damage to a product structure, does not have environmental pollution, and is suitable for large-scale industrial production.