The invention relates to the field of web pharmacy system platform and particularly relates to a method for realizing drug dismounting based on POS cash register in a pharmacy. The method comprises the steps of (1) creating a dismounting main table, a list, a drug table and an inventory batch table, wherein the main table is used for storing information such as the date of dismounting, quantity and an audit status, (2) newly creating dismounted commodity data, setting information of a unit, a coefficient, a price and the like after dismounting, and carrying out storage, (3) selecting commoditydismounting on a cashier page, inputting the information of a dismounting quantity, a price and the like on a dismounting page, and storing, (4) generating a main table and a list, adding dismountedcommodities and batch inventory, original drug total inventory reduction and batch inventory numbers, (5) changing a drug of the cashier page into dismounted drug for sale, and (6) auditing a dismounting list, updating an audit state and generating dismounting report data. According to the method, the problems that the drug is wasted when the drug is dismounted in advance when the drug is not sold, the maintenance is difficult and the dismounted drug is inconvenient to sell are solved.