Recombinant Anti-DKK1 x Anti-SOST Bispecific Antibody (Fab-Fv) is designed to be expressed as two polypeptide chains. The heavy chain Fd fragment and light chain of an anti-DKK1 antibody are fused with the VL and VH domains of an anti-SOST antibody respectively. It can form natural in vivo heterodimerization. This BsAb can bind two factors simultaneously and promote osteoblastogenesis. It is designed for the research of Osteoporosis; Osteogenesis imperfecta (OI); Low bone mineral density; Fracture therapy.