Abstract: In order to study the damage characteristics and the whole stress-strain process of soft rock under low stress, based on the damage mechanics theory and considering the impact of damage threshold on the elastic stage of rock, a damage threshold expression of soft rock was constructed by taking axial strain as the damage variable factor of rock and combining Drucker-Prager strength criterion and Hooke’s law. At the same time, the residual shear strength is introduced to describe the deformation characteristics completely. Based on Weibull distribution theory and Lemaitre strain equivalence theory, a damage constitutive model of soft rock is constructed which can reflect both the elastic stage and the residual deformation stage of low stress downline. The parameters of the theoretical model are calculated by the characteristic points of the stress-strain curve and the data of rock triaxial compression test. The nonlinear variation of peak strength, residual shear strength and confining pressure is reasonably described by exponential function. Finally, the rationality and applicability of the theoretical model proposed in this study are verified by the coal and rock test results.