The invention discloses a multi-substituent isocoumarin derivative and a preparation method thereof. According to the preparation method, substituted tert-butyl peroxybenzoate represented by a formula II, 1,2-disubstituted acetylene represented by a formula III, a catalyst, alkali, acid and a solvent are uniformly mixed and are heated under the protection of nitrogen for a cyclization reaction, and a compound represented by a general structure formula I is obtained after the reaction. According to the method, the reaction conditions are mild, the reaction time is short, the substrate range is wide, the reaction specificity is high, the yield is high, the post-processing is simple and convenient, and the multi-substituent isocoumarin derivative which cannot be synthesized with other methods can be synthesized and has a wide application.