Recombinant Anti-Ad fiber knob x Anti-CEA 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-Ad fiber knob antibody variable domain is fused to the C terminal of an IgG of anti-CEA antibody, or vice versa. The format retains desired characteristics of intact antibodies. This BsAb can retarget of adenoviral vectors to tumour cells. It can be used in cancer gene therapy to transfer a therapeutic gene into tumour cells aiming at selective and efficient cell killing.