The invention discloses a synthetic method of pholcodine. The synthetic method of pholcodine comprises the steps of deriving a phenolic hydroxyl group of a morphine base as a starting material to prolong the branch, then reacting the intermediate with an amine group on morpholine to generate crude pholcodine, and refining the crude pholcodine by means of purification to obtain pholcodine. The method is simple in reaction steps and economical and readily available in reagents, avoids the risk of using a large amount of highly toxic, flammable and explosive solvents, and greatly improves the yield and purity of the product.