The invention discloses a preparation method of sucralose. The preparation method comprises the following steps: (1) adding sucrose into N,N-dimethyl formamide, adding a catalyst, ortho-acetate, water and tert-butylamine and stirring; and conducting vacuum distillation to obtain a sucrose-6-acetate N,N-dimethyl formamide solution; (2) adding a phase transfer catalyst and a chlorination reagent into N,N-dimethyl formamide to obtain a mixture, and reacting; adding an antioxidant and the solution obtained in the step (1) into the mixture, reacting to obtain a sucralose-6-ester reaction solution; and cooling to room temperature, neutralizing, distilling, extracting, concentrating and crystallizing to obtain sucralose-6-acetate; and (3) dissolving sucralose-6-acetate in methanol, regulating the pH value, reacting, neutralizing to remove impurities, decolourizing, concentrating, crystallizing, recrystallizing and drying to obtain sucralose. The invention simplifies the reaction steps, effectively avoids excessive chlorination and polymeric reaction, improves the reaction efficiency, and is beneficial to industrial production.