The extract methods of using alk. aqueous solution to extract cantharidin from Mylabris phalerata Pallas were established.The limit of extensive use of organic solvents in the traditional process was got rid, and costs of production and environmental pollution were reduced.The yield of cantharidin and the alk. soaking times and the amount of ammonia in the impurity removal were aimed to inspect.GC was used for the determination of the extract cantharidin content.The results showed that alk. water (8, 5, 5 times) three processing Mylabris phalerata Pallas.Extracted liquid was alkalized with the ammonia equalled 2.5 times of the weight of Mylabris phalerata Pallas and the extraction has better clarity and higher yield.Through the comparison of experiment, alk. extract yield is higher than pharmacopoeia method and the method is simple, valuable and also provides the basis for large-scale production