The invention relates to the technical field of secondary metal and the field of regeneration treatment of waste aluminum, and particularly provides a method for extracting metallic aluminum from a large amount of aluminum ash generated in the regeneration process of waste aluminum. According to the process scheme, secondary aluminum ash which is subjected to thermal recovery treatment and/or conventional cold treatment is treated through a low-valency chloride-fused salt vacuum treatment method, namely, the metallic aluminum is extracted to the maximum extent with the secondary aluminum ash as raw materials and through treatment with a fusion agent and extraction with low-valency chloride. The method has the advantages that operation is easy in the melting process, the raw materials are cheap and easy to obtain, the low-valency chloride used for extracting the metallic aluminum can be recycled, and substances which can pollute the environment are avoided; and the whole process is conducted in the vacuum condition, the purity of products is high, influences on the environment are avoided, and the purity of the recovered metallic aluminum can reach 99.99%.