Knowledge of damage distribution is important and essential for understanding the dynamic failure behavior of solid material under the high velocity impact. For the High Purity Aluminum (99.999%), disk sample was shock impacted by a light gun and its damage distribution has been carefully characterized. The recovered sample was cut symmetrically along the impact direction and the damage on the cross section has been statistically studied. Unlike the previous work as Lynn Seaman et al. reported, a new computation treatment has been established in terms of the Schwartz-Saltykov method, which gives an easy and simple transformation from the two-dimensional size distribution to three-dimensional size distribution. We demonstrated the variation of damage distribution of High Purity Aluminum under different dynamic tensile loading, and discussed the damage evolution characteristics associated with the micro-voids nucleation, growth and coalescence. Results provide physical basis for the theoretical modeling and numerical simulation of spall fracture.