The tensile deformation and fracture behavior of the Ti555211 alloy with dual structure were investigated using in-situ SEM technology. Results showed that It was found that slip bands were given priority within the primary α phase along with angle of 45o with the tensile loading direction for the Ti555211 alloy with initial dual structure. As the crack propagated, the slip bands appeared dense. Moreover, the crack growth was dominant by interconnected microcavities for the alloy with initial dual structure. The Ti555211 alloy with initial dual structure and lamellar structure show different fracture morphologies. For the alloy with initial dual structure, there displayed a small flat surface causing by shear slip, but no obvious shear lip showed in fracture. The deformation and fracture behavior of the near-β titanium alloy of Ti555211 can be tracked by the SEM in-situ tensile test method in real time. The research results of this method have great theoretical value and engineering significance.