The invention discloses an application of citric acid in preparation of weak-acid electrolyzed water and a preparation method of the weak-acid electrolyzed water. The preparation method comprises the steps that a citric acid solution and a sodium chloride solution are mixed, so that a mixed solution is obtained; and the mixed solution is subjected to electrolysis, so that the weak-acid electrolyzed water is obtained. By means of the application and the preparation method, the problems that caustic diluted hydrochloric acid exists in an electrolyte solution due to incomplete electrolysis of the diluted hydrochloric acid, and the weak-acid electrolyzed water with the diluted hydrochloric acid serving as an additive is not easy to control due to the fact that the pH changes excessively fast during preparation are solved.