Recombinant Anti-CEA x Anti-DTPA Bispecific Antibody (Fab-Fv) is designed to be expressed as two polypeptide chains. The heavy chain Fd fragment and light chain of an anti-CEA antibody are fused with the VL and VH domains of an anti-DTPA antibody respectively. It can form natural in vivo heterodimerization. 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 Breast cancer; Ovary cancer; Colon cancer; Lung cancer imaging and therapy.