The invention relates to a preparation method of lycopene intermediate 3-methyl-4,4-dialkoxy-1-butyraldehyde. The preparation method comprises the following steps of: (1) under the protection of inert gas, generating a Grignard reagent mixture through the reaction between 2-methyl-3,3-dialkoxy-1-halogenated propane and magnesium powder in an anhydrous tetrahydrofuran solvent at 45-65 DEG C; and (2) then adding N,N-disubstituted formamide to the Grignard reagent mixture, reacting at 10-35 DEG C to obtain 3-methyl-4,4-dialkoxy-1-butyraldehyde. The preparation method is simple and direct in process route, is simple to operate, is mild in conditions and good in yield and has high industrial value.