A black bean milk and preparation method thereof, characterized in that the milk is made from the following materials in parts by weight:200 to 210 parts of soybeans, 200 to 210 parts of black beans, 50 to 60 parts of soy bean meal, 10 to 12 parts of spinach, 13 to 14 parts of purple sweet potatoes, 9 to 10 parts of chocolate powder, 4 to 5 parts of cistanche, 3 to 4 parts of acanthopanax senticosus, 3 to 4 parts of prepared rehmannia root, 4 to 5 parts of barbary wolfberry fruit, 2 to 3 parts of astragalus membranaceus, and 40 to 45 parts of flour. The present invention replaces part of soybeans and black beans with soy bean meal to reduce production cost. Meanwhile, soy bean meal is added with water and then magnetically stirred to make protein completely dissolve out. And soybeans and black beans are fermented before grinding, not only improving the nutritional values, but also giving a unique taste to the present invention. In addition, anthocyanin in black beans and purple sweet potatoes and cocoa polyphenol in chocolate powder can be antioxidant, and have the effect of anti-aging collocated together with Chinese medicine in the present invention.