Bone morphogenetic protein(BMP)- 9 belongs to the BMP family，which mediate the osteogenic differentiation of mesenchymal stem cells，muscle cells and preosteoblasts，and promote chondrogenesis. The mechanism of osteogenic differentiation induced by BMP-9 is not identical to that of traditional bone morphogenetic proteins(BMP-2，BMP-4，BMP-7，etc.). The ability of BMP-9 to induce osteogenic differentiation of mesenchymal stem cells was significantly stronger than other BMP(such as BMP-2，BMP-4， BMP - 7，etc.). The traditional BMP inhibitor Noggin has no significant inhibitory effect on the ability of BMP - 9 to promote bone differentiation. In this review，the structure and receptor of BMP-9，the function and signaling mechanism of osteogenic differentiation， and chondrogenic differentiation are reviewed，and the development prospect of BMP-9 is prospected.