The deformation and fracture of a third generation single crystal superalloy during in-situ tensile at room temperature was investigated at multiple scales by Scanning Electron Microscope (SEM), Electron Back-Scattered Diffraction (EBSD) and Transmission Electron Microscope (TEM) to reveal the deformation and fracture mechanism during tensile. The proportion of Low Angle Boundaries (LABs) with angle from 2.5° to 5.5° increases during tensile. The change of LABs is particularly pronounced after 7% elongation. The initiation of micro cracks is caused by {111}<110> slip systems. After initiation, the crack size along the stress direction increases while the size extension along slip systems is suppressed. The fracture mode of the alloy is cleavage-like and slip lines near the fracture are implicit at room temperature.