In this paper, a new kind of damage evolution equation is presented by the method of phenomenological analysis and microscopic statistics. And on the basis of this several spallation criterions are established, which are used easily in engineering. By the numerical simulations of the free surface velocity histories and based on the best consistence between the computational results and the experimental ones, the material parameters in the damage evolution equation and the spallation criterion are obtained. The satisfactory agreement between the computational results and the experimental ones show that the new form of damage evolution equation and the spallation criterion are reasonable, and the method of determining the material parameters is effective.