Abstract：Based on rock damage model founded by Lemaitre¢s strain equivalent theory，the changing rule of damage variable or damage factor during the process of rock strain softening deformation，the characteristics of rock strain softening，the rock damage mechanism and the necessity of considering the influence of the damage threshold in developing rock damage evolvement model are discussed. Then，a new method for measuring microcosmic element strength of rock is presented with consideration of damage threshold；and a new statistical damage evolvement model is established by adopting statistical damage theory. This model can reflect not only the influence of damage threshold but also the influence of stress states on damage degree of rock as well as the damage characteristics of different initial points under different stress states. Based on these，a damage statistical softening constitutive model used to simulate the rock strain softening deformation process is developed；and the method to determine the model parameters is proposed. This model can reflect the linear-elastic characteristics of rock deformation in low stress level or small deformation. Moreover，the concepts of the model parameters are clear；and it is convenient for the model to be applied to complex stress state cases. Finally，the case study indicates that the constitutive model is reasonable.
