Recombinant Anti-CEA x Anti-DTPA Bispecific Antibody (scFv-CH3) contains two chains. The anti-CEA scFv is fused to the Knob-CH3 domain via a hinge region and the same as the anti-DTPA scFv to the Hole-CH3 domain, or vice versa. The KIH CH3 domains can facilitate to form a heterodimer and this bivalent binding leads to improvement in avidity. 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.