The deformation and fracture of a third-generation single crystal superalloy during in-situ tension at room temperature were investigated at multiple scales by scanning electron microscope, electron back-scattered diffractometer, and transmission electron microscope to reveal the deformation and fracture mechanism during tension. The proportion of low angle boundaries (LABs) with angles from 2.5° to 5.5° increases during tension. The change in LABs is particularly pronounced after elongation over 7%. The initiation of microcracks is caused by {111}<110> slip systems. After initiation, the crack size along the stress direction increases whereas the size extension along slip systems is suppressed. The fracture mode of the alloy is quasi-cleavage fracture and the slip lines near the fracture are implicit at room temperature.