Method for preparing secoisolariciresinol diglucoside

The invention discloses a method for preparing secoisolariciresinol diglucoside (SDG), which comprises the following steps of: 1) crushing linseeds, extracting by using ethanol aqueous solution, and concentrating extracting solution to obtain concentrated solution; 2) adding alkaline aqueous solution into the concentrated solution, hydrolyzing at the temperature of between 50 and 80 DEG C for 30 to 40 minutes, cooling, regulating the pH to 3.5 to 4.5 by adding acid, standing for 30 to 40 minutes, centrifuging and collecting supernatant; and 3) adsorbing the supernatant through a macroporous resin column, washing the resin column until effluent liquid is not saline, eluting by using 25 to 50 volume percent ethanol aqueous solution, collecting the eluent, concentrating under reduced pressure and drying to prepare the SDG. The method is simple in process and is easily controlled, the extraction time and the hydrolysis time are greatly reduced, the production cycle is effectively shortened, the quality requirement of a product obtained by the method is met, the SDG content in the product is 30 to 50 percent, and the product yield is 3 to 5 percent.