The invention discloses a preparation method of a water soluble crystal rich in metasilicic acid, wherein the preparation method comprises the steps: a first step, crushing crystal stone down with a stone crusher, putting in an ultrasonic device, and carrying out ultrasonic cleaning; a second step, putting the cleaned crystal stone in a high temperature furnace, wherein the high temperature furnace totally has two chambers divided into a chamber A and a chamber B; a third step, rising the temperature to 1700-1800 DEG C, and in the process of complete gasification of the crystal stone, blowingcrystal stone gas to one of the chambers, to reach the purpose of removing impurities and achieving an essence; a fourth step, in one chamber of the crystal stone gas in the third step, dropping the temperature to 1200-1400 DEG C, making the crystal stone show a molten state, and carrying out a mixed reaction of the crystal stone with caustic soda placed in the chamber, wherein the reaction time is 2-3 hours; and a fifth step, dropping the temperature to room temperature according to a way of dropping 100 DEG C in every 5 minutes, to obtain a white crystal. The preparation process of the watersoluble crystal rich in metasilicic acid is well controlled, and the water soluble crystal rich in metasilicic acid can be prepared in batches and can release large amounts of metasilicic acid to water bodies.