The invention relates to a method for preparing a multifunctional power coating additive with a core-shell structure. The method comprises the steps of: A. uniformly mixing butyl methacrylate (BMA), methyl methacrylate (MMA) and lauryl mercaptan as a core monomer; B. uniformly mixing butyl methacrylate (BMA), methyl methacrylate (MMA), glycidyl methacrylate (GMA) and lauryl mercaptan as a shell monomer; C. adding water, lauryl sodium sulfate and sodium bicarbonate in a reactor, uniformly stirring to raise temperature, dripping the core monomer and ammonium persulfate, and maintaining the temperature; dripping the shell monomer and ammonium persulfate, and maintaining the temperature; cooling and filtering to obtain white acrylic ester core-shell polymer latex, wherein the solid content in the latex is 40-50%, and the conversion rate of the monomer is higher than 90%; and D. adding a calcium chloride aqueous solution, separating, washing with water, and drying to obtain a white powdery solid product. The additive is used for power coatings without being molten and granulated, can be added directly for use, and has the environmentally friendly characteristic.