Preparation method for apremilast and intermediate of apremilast

The invention relates to a preparation method for apremilast and an intermediate of the apremilast. The preparation method comprises the following steps: enabling 4-methoxy-3-ethoxybenzaldehyde to have Mannich reaction with methylsulfonylmethane and ammonia under the action of L-proline and a promoter to obtain an intermediate, (S)-1-(4-methoxy-3-ethyoxyl)phenyl-2-(methylsulfonyl)ethylamine (II), and then amidating the intermediate (II) and 3-acetamido-phthalic anhydride to prepare the apremilast (I). According to the preparation method for the apremilast and the intermediate of the apremilast, the raw materials are easily available, the flow path is short, the process is simple and convenient, the product has high optical purity, and the industrial production is safe and environmentally friendly.