The invention relates to a synthesis method of alvimopan. The method comprises the steps of taking the compound A of an acetyl protection piperidine fragment as a raw material and reacting with (S)-ethyl-2-(2-benzyl-3-methyl sulfonoxy alanyl)-acetic acid, then performing one-step basic hydrolysis to prepare the alvimopan. In the technical solution, the synthesis method has the advantages of mild production conditions, simple production process, less side reactions, high product yield, high purity and the like, and is suitable for industrialized large-scale production.