Provided are bifidobacterium lactis BL-99 capable of improving immunity and application thereof. The Bifidobacterium lactis BL-99 was deposited in the China General Microorganisms Collection Management Center (CGMCC) on April 26, 2018 with a deposit number of CGMCC No. 15650, has gastric acid resistance and intestinal fluid resistance, can significantly promote the growth of bifidobacteria and lactic acid bacteria, can significantly increase antibody-producing cells and half hemolysis value HC 50 , activate NK cell activity, can be used for preparing foods that improve immunity, and has the effects of preventing osteoporosis and improving blood calcium and/or phosphorus ions.