Method for extracting cantharidin from cantharides

The invention relates to a method for extracting cantharidin from cantharides. The method is characterized by comprising the following steps of: performing continuous countercurrent ultrasonic extraction on powder of cantharides by using acetone, removing impurities from an extracting solution, concentrating under reduced pressure, evaporating to remove partial solvent, and cooling and crystallizing a concentrated solution to obtain a crude product of cantharidin; heating to dissolve the crude product by using chloroform, filtering to remove insoluble substances, and cooling and crystallizing filtrate to obtain the cantharidin. The continuous countercurrent ultrasonic extraction is adopted, the impurities are removed from the extracting solution by an elutriation method, and recrystallization is carried out by using the chloroform, so that the cantharidin with the content of over 98 percent is obtained, steps of degreasing by using an organic solvent and the like are eliminated, the operation is simple, the production is safe, the extraction yield is high, and the method is suitable for mass production.