This paper presents two evolution laws for dynamic tensile damage of brittle rock based on light gas gun (LGG) tests. By analyzing the attenuation of sound-wave propagation in the rock samples before and after impact tests, one evolution law for dynamic tensile damage of rock is introduced and incorporated into the finite element code LS-DYNA through a user-defined subroutine. The improved code is then applied to the simulation of the tensile damage and blast crater near free face of rock mass, and the resulting crater geometry is compared with empirical formula. In addition, based on the phenomenological point of view and the velocity–time histories recorded in LGG tests, another evolution law of tensile damage is proposed to consider the nucleation and growth of microflaws in rock. Parametric analyses are carried out with the self-developed finite difference code and an optimization procedure for the parameter determination is suggested.