The invention relates to a substance which is extracted from giant knotweed for curing 
diabetes mellitus and complicating diseases. By using the substance extracted from the giant knotweed, the 
medicine for curing 
diabetes mellitus and the complicating diseases can be produced effectively, and the treatment problems of 
diabetes mellitus and the complicating diseases are solved. The substance is coarse 
powder of the giant knotweed and can be prepared through the following steps: putting the giant knotweed in a round flask, adding 6 times quantity of grain 
alcohol to soak the giant knotweed; refluxing and extracting and filtering the grain 
alcohol, and the 
reflux extraction and the filtering are carried out to medical 
slag which is added with the grain 
alcohol which is 6 times of the medical 
slag. The filtrate water are combined for two times, the filtrate water is decompressed for recycling the grain alcohol, and the filtrate water is added in the pretreatment and reborn 
macro pore adsorption resin column; the resin column is elutriated with 
distilled water until the eluate is colorless, and the resin column is elutriated with the grain alcohol, the 
mass concentration of which is 70 percent, the eluate is collected till the eluate does not contain any component of 
anthraquinone, and the grain alcohol is recycled, and the total 
anthraquinone which is the extracted substance of the giant knotweed can be gained when the eluate is volatilized on the water bath. The invention has the advantages that the preparation method of the product is scientific, the operation is easy, the quality of the total 
anthraquinone which is the preparation substance is good, the purity quotient is high and the effect is good. The substance can be used for preparing the 
medicine which is used for curing diabetes mellitus and the complicating diseases, and the substance which benefits mankind is a creative of the development and the application of the giant knotweed 
medicine.