Recombinant Anti-FN1 x Anti-HSG Bispecific Antibody (Fv-IgG) is an appended IgG format, which has 2+2 antigen-binding valency. This dual variable domain IgG is generated by appending variable domains of an anti-FN1 IgG with similar domains from an anti-HSG antibody via short peptide linkers, or vice versa. This BsAb can be used in pretargeting system of PET, radioimaging or radiotherapy. It can mediate targeting of radioactivity to tumor cells. It is designed for the research of Solid tumors imaging and therapy.