The invention discloses a method for extracting alpha-mangostin from garcinia mangostana peel. The method includes the following steps that 1) the garcinia mangostana peel is crushed, reflux extraction is conducted once or twice with water of 8-10 times of weight, then reflux extraction is conducted for one to three times with a 90%-95% ethanol solution of 8-10 times of weight, an extracting solution of the ethanol solution is combined, the extracting solution is concentrated to be twice or three times of the weight of the garcinia mangostana peel, centrifuging is carried out, and after centrifugal residues are dried, a crude extract is obtained; 2) subcritical extraction is conducted by using the fluid which is formed by dimethyl ether and butane according to the weight ratio of 60-70 : 30-40 as an extraction agent, the extraction temperature is 68-72 DEG C, the extraction pressure is 2.8-3.2MPa, and the extraction time is 20-40min. According to the method for extracting the alpha-mangostin from the garcinia mangostana peel, water extraction and alcohol extraction are used for obtaining the crude extract first in the extracting process, the content of the alpha-mangostin of the crude extract is 70%-80%, then subcritical extraction is conducted, and the content of the alpha-mangostin is further made to reach 98%. The method is short in time, small in dosage of reagents, simple in step and high in yield and content, a subcritical extraction agent is volatilized directly to obtain a product, and thus the method is more suitable for industrial production.