The invention provides a method for improving the cleanliness of low-carbon molten aluminum-killed steel, which belongs to the technical field of killed steel. By adopting two-step smelting process of converter molten iron dephosphorization and less-slag decarburization steel making, a converter has low endpoint oxygen content, deoxidized molten steel has less original impurities, and the control is executed at the very beginning of the impurities generation. Top slag of ladles is modified to slag with stronger capacity of adsorbing the impurities, the fully upward floatation of the impurities is ensured by emphasizing slag-free operation in a CAS refining cover and a longer pure argon blowing time, adopting a high-alkalinity covering agent and special protecting slag for a crystallizer for continuous casting is beneficial to impurity adsorption, and then the impurities are removed by adopting measures in each point where the impurities are generated. By adopting the method, the T.O content of molten steel in ladles is not more than 30ppm, and the molten steel has high cleanliness and good continuous castability. The method has the advantages of reasonable process and low production cost.