The present invention relates to a synthesis process of suvorexant, novel compounds represented by formulas II, III, IV or V, or salts thereof for preparing suvorexant, and a method for preparing the intermediates. The preparation method uses a chiral starting material to synthesize chiral compounds represented by formulas II, III, IV or V, the compounds obtained being used for synthesizing the suvorexant. The preparation method has the advantages of simple operation, low cost, mild reaction conditions, simple post-treatment, easy to purify, high yield, high ee value for the product, and easy to industrialize. In the reaction route shown, R represents benzyl, allyl or 1-phenethyl, or optionally substituted benzyl at the 2 position to 6 position, such as 4-methoxybenzyl, 4-nitrobenzyl, 2-methylbenzyl, 4-chlorobenzyl or 3-fluorobenzyl.