Disclosed is a preparation method of the lycopene intermediate 3-methyl-4,4-dialkoxy-1-butaldehyde. The preparation method comprises the following steps: (1) reacting 2-methyl-3,3-dialkoxy-1-halopropane with magnesium powder in the solvent of anhydrous tetrahydrofuran at a temperature of 45˜65° C. to generate a mixture of Grignard reagents under the protection of an inert gas; and (2) adding N,N-disubstituted carboxamide to the mixture of Grignard reagents and reacting at a temperature of 10° C.˜35° C. to obtain 3-methyl-4,4-dialkoxy-1-butaldehyde. The process route of the present invention is simple and direct, the operation is easy, the conditions are mild and the yield is good, and thus the invention has commercial value.