Recombinant Anti-Ad fiber knob x Anti-CEA Bispecific Antibody (Tandem scFv-Fc) is designed to be expressed as a homodimer, which has 2+2 antigen-binding valency. This format consists of one Fc region and two tandem scFv fragments, in which the anti-Ad fiber knob/CEA tandem scFv is fused to the Fc domain. The engineered fragment format is used to extend the half-life. 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.