Abstract: In-situ tensile tests at 300℃ of laser melting deposited (LMD) TA15 alloy were carried out by in-situ high temperature scanning electron microscopy-electron backscattering diffraction (SEM-EBSD) mircotensile system. The microstructure evolution and fracture mechanism of the alloy during in-situ tension were studied. The results show that slip was the main plastic deformation mechanism in the LMD TA15 alloy during tension at high temperature. The crack propagation path was consistent with the slip band propagation path, and both propagated by cutting through the α strip cluster. The fracture of the alloy presented the brittle-ductile mixed fracture mode, and the existence of β grain boundaries was the root cause of local brittle fracture. In the early stage of deformation, grains rotated, and uniform plastic deformation of the alloy occurred. With increasing strain, there were a lot of low-angle grain boundaries in local grain by dislocation, and the fraction of low-angle grain boundaries increased from 4.9% before tension to 33.7% at the strain of 12%; inhomogeneous deformation of the alloy occurred.