The invention discloses a method of recycling dextromethorphan from a crystallization mother liquid. The method is characterized in that with the crystallization mother liquid as an initial raw material, pre-treatment of impurities, high-pressure crystallization, washing, filtration and drying are carried out to obtain a dextromethorphan crude product (final product purity being 95.0-98.0%). In the novel purifying process, the advanced high-pressure crystallization is applied so as to solve the difficult technical problem that the crystallization mother liquid is difficult to recycle well. The method not only greatly increases the total yield of the dextromethorphan but also is simple in operations and is suitable for industrial production.