The invention provides flatstem milkvetch seed oral liquid for improving immunity. The flatstem milkvetch seed oral liquid is prepared from the following raw materials in parts by weight: 10-50 parts of flatstem milkvetch seed, 10-20 parts of mulberry, 10-20 parts of Chinese angelica, 10-20 parts of prepared rhizome of rehmannia, 10-20 parts of astragalus membranaceus, 10-20 parts of glossy privet fruit, 10-20 parts of semen cuscutae, 10-20 parts of rhizoma polygonati, 10-20 parts of radix codonopsis, 10-20 parts of poria cocos, 10-20 parts of fructus alpiniae oxyphyllae, 10-20 parts of human placenta, 10-20 parts of dogwood, 10-20 parts of raspberry, 10-20 parts of radix paeoniae rubrathe (unpeeled) root of common peony, 10-20 parts of bighead atractylodes rhizome, 10-20 parts of dendrobium, 10-20 parts of Chinese magnoliavine fruit, and 10-20 parts of rhizoma acori graminei. The oral liquid uses the flatstem milkvetch seed as raw materials, and the traditional Chinese medicines which nourish liver and kidney, have moderate mouth feel and are easily accepted by people are added, so that the immunity can be obviously improved, and the situations that sub-health crowds are easy to have a cold, the eyes of the sub-health crowds are acerb, the sleep quality of the sub-health crowds is not high, and the sub-health crowds have splenic asthenia and weakness can be better improved; the oral liquid can alleviate the symptoms of reduced appetite, dry mouth, drinking and urine, deficiency of the kidney, soreness and weakness of waist and knees, impotence and seminal emission, tinnitus and blurring vision, premature graying hair, weak health and emaciation, leprosy and ringworm diseases; the oral liquid does not have toxicity or stimulus, so that the oral liquid is suitable for people to take for a long term.