The invention belongs to the technical field of new material preparation and relates to an economical and practical method for preparing YAG monocrystal powder to solve the problems that in an existing hydrothermal-method preparation process, harsh conditions of high temperature and high pressure are needed and yield is low. The method comprises the six process steps of material matching and briquetting, block melting, product precipitation, frit smashing, powder separating and powder purifying. A common silicon carbide rod batch-type furnace is used for replacing an existing high-temperature and high-pressure autoclave, preparation of the YAG monocrystal powder under the normal pressure is achieved, particles in the prepared powder are non-conglobatus monocrystals growing well, and the whole process is carried out under the normal pressure in air. The whole process is simple, preparation conditions are easy to get, the preparation cost is low, the product performance is good, the application range is wide, and environmental friendliness of industrial production is achieved.