The invention relates to a polysubstituted isoxazolidine derivative and a preparation method thereof. The structural formula of the polysubstituted isoxazolidine derivative is as shown in a Formula (I) in the specification, wherein R1 and R2 are substituted aryl or alkyl; a substituent group on Ar can be alkoxy, halogen or alkyl; the substituted aryl is phenyl or naphthyl; and the alkyl generally comprises methyl, ethyl and cyclohexyl. The preparation method comprises the following steps: at room temperature, in an air or nitrogen atmosphere, dissolving a nitrone derivative as shown in a Formula (II), an olefin structure-containing compound as shown in a Formula (III) and a photocatalyst as shown in a Formula (IV) in an organic solvent, performing uniform mixing, performing illumination under blue LED lamps or filament lamps for hours; and after the reaction is completed, performing rotary evaporation on the solvent, and performing separation and purification through silica gel column chromatography to obtain the polysubstituted isoxazolidine derivative. The method solves the problems of need of a high temperature heating system, high energy consumption, strict conditions and high equipment requirements in the existing isoxazolidine derivative synthesis process; and the method is mild in conditions, simple, convenient to operate and high in yield.