Abstract: The reasonable synthetic mode of stress and strain for complex theory of geomaterial damage was obtained based on the basic concept of continuum mechanics.The simplified formulas of synthetic mode of stress and strain for isotropic damage was provided.A constitutive model for isotropic damage of geomaterials was put forward,and its numerical computation procedure was also given.The calculated results for a simple example could highlight our understanding about the mechanism of geomaterial damage,and several useful conclusions could be drawn: The series assumption could not be used to the synthetic mode of stress and strain for complex theory of geomaterial damage;strictly speaking,the parallel assumption could not be used to the synthetic mode of stress and strain even under small strain;the complex stress-strain behavior was similar to that of ideal natural geomaterials under small stress,and varied with stress path under large stress.