The invention discloses high-liquidity starch and a preparation method and the application thereof. The preparation process is simple, reaction is uniform, production cost is low, reaction time is short, expansion of starch particles under the alkaline reaction condition is restrained by sodium sulfate to avoid starch gelatinization and enable starch chemical modification to be centralized on the particle surfaces; introducing an ultrasonic field into the reaction process can improve reaction efficiency, reduce usage of chemical agents, shorten reaction time and reduce cost; electronegative substitute groups are crosslinked by metallic ions of different valences, a great amount of hydroxyls on the starch particle surfaces are shielded, and accordingly angle of repose of starch can be evidently decreased, and liquidity is improved. High-fluidity starch with the angle of repose ranging from 2 degrees to 5 degrees is obtained and has wide application values in industries of foods, daily chemicals, printing, agriculture, petroleum and the like.