The invention discloses 3,3-disubstituted oxoindole and a preparation method thereof. Reaction comprises the following steps that an alkenyl active methylene compound is used as a substrate, a metal hydride is used as a reducing agent, a palladium compound is used as a catalyst, and reduction reaction is carried out to obtain a reduction product; the reduction product is reacted with an electrophilic reagent to obtain the 3,3-disubstituted oxoindole. A reduction system of the preparation method of the 3,3-disubstituted oxoindole is a simple method for reducing the alkenyl active methylene compound, both the adopted hydride and palladium compound catalyst are reagents easy to obtain in a laboratory, and compared with a common hydrogen hydrogenation method and reducing agent reduction method, the method is more easy to operate, higher in safety, mild in condition, high in reaction yield and capable of one-pot two-step reaction, and has very high atom economy and step economy.