The present invention relates to a method for preparing dried alpha-rice by vacuum drying comprising: (a) washing out impurities from the surface of hulled-rice by using a washing device; (b) immersing the washed rice in water for 3 to 120 minutes to contain water uniformly, and then drying it naturally for 3 to 30 minutes; (c) putting the soaked rice into an auto conveyor rice cooker, wherein the temperature of water is maintained at 80 to 98% C, and then scalding it for 8 to 20 minutes to be boiled rice; (d) cooling the boiled rice rapidly by shower at first, and then washing out it in a cooling tank secondly; and (e) putting the boiled rice into a vacuum drying room, which temperature is maintained at 60 to 98% C, and reducing the internal pressure to below 1 Torr, and then vacuum drying the boiled rice until its water content becomes less 5%.