The present invention relates to a preparation method for an antibacterial agent. The method comprises the following steps: weighing a certain amount of praseodymium oxide, deionized water, nitric acid, and hydrogen peroxide, and adding the materials to a reaction vessel to form Pr(NO3)3.6H2O; weighing a certain amount of sodium 2-hydroxyphenylacetate, ethanol, deionized water, 5-chloro-7-hydroxyquinoline, and Pr(NO3)3.6H2O, performing a reaction on the materials to obtain a solution A; adjusting a pH value of the solution A with nitric acid or sodium hydroxide, and performing steps of washing, pumping filtration, drying, grinding, and sieving to obtain the antibacterial agent. The Pr ion has the function of antagonizing intracellular calcium ions, and calcium ions are ions that maintain the normal physiological activity of cells, which interfere with the normal life activities of bacterial cells and cause bacterial death; the addition of the special antibacterial agent enhances the antibacterial properties of polymer composites, and the antibacterial agent has great promotion value.