The invention discloses a preparation method of a medicament for treating diabetes and belongs to the preparation method of a medical preparation which contains raw materials derived from traditional Chinese medicaments. In the preparation method, membranous milkvetch root is processed by cellulose and then is subjected to alcohol circumfluence extraction; golden thread and honeysuckle flower areprocessed by the cellulose and pectinase respectively and then subjected to cold extraction. Compared with the conventional extraction method, the preparation method improves extraction rate of totalsaponins of the membranous milkvetch root by 30 to 50 percent, improves extraction rate of berberine and total alkaloid by 20 to 40 percent, and improves yield of chlorogenic acid by 15 to 30 percent, and 30 to 50 percent respectively. The preparation method improves transference rate of effective substance in plant medicinal materials and can fully use medicinal material resources.