The invention discloses a method for synthesizing alumina nano powder, which comprises: firstly, dissolving aluminum inorganic salt into deionized water, and adding a dispersant for stirring and mixing; secondly, dissolving copper nitrate, manganese nitrate and tetrabutyl titanate into absolute ethyl alcohol, and using concentrated nitric acid and acetic acid to adjust the pH value to be between 2.5 and 4.5; thirdly, uniformly mixing the two solutions, placing the mixture in a water bath or an oven at a temperature of between 80 and 100 DEG C, and obtaining dried gel after a period of time; and fourthly, placing the dried gel into a high-aluminum crucible, and roasting the dried gel at a temperature of between 800 and 1,100 DEG C to obtain the alumina nano powder. Raw materials adopted by the method have wide sources and low cost, and are easily obtained; the preparation technology is simple and controllable; the high-temperature stable alpha-Al2O3 nano powder with fine particle diameter, uniformly distributed particles and single crystal phase can be synthesized at a low temperature; and the prepared alumina nano powder is used for preparing alumina ceramics, and has the advantages of obviously saving energy and reducing consumption because the sintering temperature can be reduced to be less than 1,250 DEG C.