The invention discloses a millettia extract and a preparation method and the application thereof. 45 to 55 percent of ethanol is added into millettia medicine to be extracted and is loaded to a macroporous absorption resin column, and is eluted sequentially by water, 10 to 30 percent of ethanol and 65 to 75 percent of ethanol. 65 to 75 percent of ethanol is used for eluting a part, the ethanol isrecovered and evaporated to dryness to obtain the millettia extract. Based on a tradition preparation method, the preparation method of the millettia extract designs reasonably and obtains an optimized production process combination, and the millettia extract obtained by the preparation method has high yield and more singificaly improves the functions of leukocytes compared with the millettia extract obtained by the traditional preparation method.