Recombinant Anti-FN1 x Anti-HSG Bispecific Antibody (Fab-IgG) is designed to be expressed as three chains, assembling in vivo and resulting in the construct of Fab-IgG (Tandem Fab-Fc). Fab-IgG has standard Fab and Fc domains, with no mutations, which may permit it has similar affinity binding and PK profile comparable to the parental antibodies. 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.