The invention relates to the technical field of cannabidiol, and in particular relates to a method for extracting cannabidiol (CBD) by combining tunnel ultrasound and thermal circulation distillation.The method comprises the following steps (1) pretreating raw materials; (2) mixing the materials; (3) extracting by tunnel ultrasonic wave and heating combined extraction equipment; (4) putting extraction liquid into a circulating single-effect concentration tank, performing primary concentration, and recovering ethanol; (5) heating a concentrated solution obtained in the primary concentration, and continuing secondary concentration; (6) redissolving secondary concentrated extract, filtering and concentrating; (7) performing silica gel chromatography; (8) performing reverse silica gel chromatography; and (9) performing crystallization. According to the invention, the cannabidiol (CBD) is extracted through the combination of tunnel ultrasound and thermal circulation distillation, so that the extraction efficiency, yield and purity of the CBD can be improved, other phenolic compounds can be effectively removed, and the method is suitable for large-scale production of the CBD.