Method for extracting alkaloid from Kratom

The invention discloses a method for extracting alkaloid from Kratom, which comprises the following steps of: 1) smashing Kratom leaves, extracting with 90 to 95 percent ethanol at normal temperature, combining extracts, and concentrating to obtain concentrate; 2) adding ethanol into the concentrate until the ethanol concentration is 90 (mass) percent, standing for 1 to 3 hours, centrifuging, collecting supernate, concentrating until alcohol is removed completely, and obtaining concentrated supernate; and 3) extracting the concentrated supernate with ethyl acetate for 1 to 3 times, re-extracting with chloroform for 1 to 2 times, concentrating the chloroform extract, removing the chloroform, freezing and drying to obtain Kratom alkaloid extract. The method is simple and easy to control, the total mass of the alkaloid in the obtained extract is more than 70 percent (assayed by High performance liquid chromatography (HPLC)), and the yield is 0.6 to 0.8 percent.