The invention relates to a method for preparing nano-alumina reinforced aluminum-based composite semi-solid slurry based on a composite vibration technology. The method comprises the steps: mixing nano alumina and aluminum powder according to the mass ratio of (1: 1) to (1: 2), carrying out ball milling for 45-50 hours at the revolving speed of 50-60rpm, then, adding magnesium powder, and carrying out ball milling for 20-25 hours so as to obtain mixed powder, wherein the mass ratio of nano alumina to aluminum powder to magnesium powder is (4: 4: 3) to (4: 8: 3); melting aluminum alloy in a clay crucible so as to obtain aluminum alloy melt, and carrying out heat preservation for 10-15 minutes at the temperature of 720-750 DEG C; cooling the aluminum alloy melt to a semi-solid temperature range, adding the mixed powder into the aluminum alloy slurry at the speed of 1-1.5g/min in accordance with that the addition amount of the nano alumina is 1-5wt.% of the amount of the aluminum alloy slurry, meanwhile, carrying out mechanical stirring at the revolving speed of 300-400rpm, and then, re-stirring for 15-20 minutes; heating the slurry to the temperature of 680-700 DEG C, treating with ultrasonic sound of 20KHz and 1,000W for 5-10 minutes, then, cooling the melt to the semi-solid temperature range at the cooling speed of 5-15 DEG C/min, and treating with ultrasonic sound of 20KHz and 600-1,000W. According to aluminum-based nano composite material tissue prepared by the method, a newborn alpha-Al phase is fine and is uniform in distribution, nano alumina particles are uniform in distribution and are free from an agglomeration phenomenon, and the method is low in process cost and convenient in operation and is safe and reliable.