Ad fiber knob CD40 scFv IgG: Recombinant Anti-Ad fiber knob x Anti-CD40 Bispecific Antibody (scFv-IgG) is formed by an IgG and two scFv fragments. The scFvs from an anti-Ad fiber knob antibody variable domain are respectively connected to the N terminus of the anti-CD40 IgG heavy chains or light chains to form scFv-(H)IgG or scFv-(L)IgG. It is a type of appended IgGs and has 2+2 antigen-binding valency. 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.