B7 is a members of immunoglobulin superfamily and are expressed in many immune cells and non immune cells. When B7 is on the surface of antigen presenting cell is engated by its receptor on T cells, it provides critical positive second signals that regulate the activation, proliferation and responses of the T cells. B7 family members also play a vital role in the pathogenesis of infections,tumors,and autoimmunity diseases etc. Selectively interrupting the costimulatory molecules may be a new way in the clinical treatment of these diseases. In recent years, the newly discovered members of B7 family such as B7H3 ,B7H4 and B7H6 make the family more and more diverse. In addition,the recognition on the characteristics of B7 family may provide a better prospect for the clinical treatment of related diseases.