Recombinant Anti-CD28 x Anti-CD3 Bispecific Antibody (IgG-Fv) is formed by an Immunoglobulin G (IgG) and a fragment variable Fv region, in which the Fc of IgG is engineered by KIH. The Fv region of an anti-CD28 antibody variable domain is fused to the C terminal of an IgG of anti-CD3 antibody, or vice versa. The format retains desired characteristics of intact antibodies. This BsAb can improve T-cell activation. It is designed for the research of Tumors therapy.