By molecular dynamics method, the tensile processes of nano-single crystal copper with the type I crack under different temperature were simulated, and the effect of different temperature to crack propagation mechanism was analyzed. The results indicate that the temperature has significant effect on crack propagation mechanism of nano-single crystal copper. While the crack is the intrinsic brittle cleavage extension under low temperature and room temperature, the twin crystal is not easily to generate; whereas, dislocation climb caused twin crystal belt appears near the crack tip under high temperature. With load increasing, the length and the width of twin crystals belt increase gradually, and the existence of the twin crystal belt causes the crack branch change to the extending direction.
