Under shear load, crack propagation and microstructural evolution of Ni-based single crystal alloy have been investigated by molecular dynamics simulations. Stress-strain, potential energy and crack growth rates have been explored. Moreover, the influences of temperatures and strain rates have been verified. Simulation results show that the critical stress value increases with the decreasing temperature and increasing strain rate, respectively. As the temperature increases, the crack propagation is accelerated by severe thermal vibrations. Then, dislocations pile-up and twinning emerge resulting in significantly work hardening at a higher strain rate.