The invention belongs to the field of inorganic nonmetallic material preparation process technology, and discloses a mixed microwave sintering method of alpha-AL203 powder. The method comprises the following steps: putting precursor powder in an auxiliary heating insulation device, putting both the auxiliary heating insulation device and the precursor powder in a microwave cavity for sintering, firstly, turning on the microwave source, adjusting the microwave input power, and slowly heating up at an average speed of 6-30 DEG C / min; after dewatering, continuously adjusting the microwave input power, rapidly heating up at a speed of 20-100 DEG C / min, and meanwhile monitoring the reflection power; and after the reflection power is stable, maintaining the heating rate at 10-30 DEG C / min, heating up to a sintering temperature of 1000-1500 DEG C at a constant speed, keeping at the temperature for 2-20min, controlling the microwave input power, and rapidly cooling to room temperature at a constant speed of 6-30 DEG C / min to obtain alpha-AL203 powder product. The method of the invention combines traditional sintering and microwave sintering according to the wave adsorption property of oxides, so as to realize rapid sintering of alpha-AL203 powder. The method is low in cost, pollution-free, convenient and rapid, and is suitable for large-scale production of alpha-AL203 powder.