Recombinant Anti-Ad fiber knob x Anti-CEA Bispecific Antibody (scFv-CH3) contains two chains. The anti-Ad fiber knob scFv is fused to the Knob-CH3 domain via a hinge region and the same as the anti-CEA scFv to the Hole-CH3 domain, or vice versa. The KIH CH3 domains can facilitate to form a heterodimer and this bivalent binding leads to improvement in avidity. 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.