The invention relates to a preparation method of a mineralization material for purified water subjected to reverse osmosis. The preparation method comprises washing, drying, calcining, cooling and crushing shells, crushing periclase, putting the shell coarse powder and periclase coarse powder into a container, adding water into the container in batches, carrying out grinding to obtain paste, adding lactic acid in the paste-type suspension in batches, carrying out uniform stirring in a water bath, discharging the suspension, collecting the suspensions in multiple processes, heating the collected suspensions to evaporate water, and carrying out cooling to precipitate crystals which are mineralization materials when the suspensions form paste. The preparation method can prepare the mineralization material rich in calcium lactate and magnesium lactate. Through the characteristic of very small solubility of calcium lactate and magnesium lactate in cold water, the mineralization material can mineralize purified water subjected to sea water desalination and prevent the defects of the traditional mineralization method. The preparation method has simple processes and a high material conversion rate and realizes a low production cost. The mineralization material prevents phenomenon of mineral deficiency in the human body and protects municipal water supply pipes.