Recombinant Anti-Ad fiber knob x Anti-CEA Bispecific Antibody (scFv-CH1/CL) is designed to be expressed as two chains. One scFv from an anti-Ad fiber knob antibody variable domain is fused to CH1 and the other scFv from an anti-CEA antibody variable domain fused to CL, or vice versa. And the CH1 and CL domains are linked covalently via a natural disulfide bond. 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.