According to research on mode Ⅰ and mode Ⅱ crack damage coupled with fractures, a damage evolution equation that is more suitable for mode Ⅱ cracks was established based on the damage equation of a mode Ⅰ crack. Then, the calculation method for the damage area was obtained. The variation of the direction in which the crack developed was studied using the damage gradient, over a period ranging from damage to cracking of the mode Ⅱ crack. Finally, the propagation angle of the mode Ⅱ crack was determined to be 79°. This propagation angle was compared with that obtained by the classic criterion. The results show that the method used in this study is feasible.