Abstract:The equivalent strength parameters of rock mass(composite medium) are studied from the viewpoint of energy equivalence. Based on the equivalence of the plastic complementary energy,the equivalent computational expression is derived,which shows the correlation between deformation parameters and strength parameters. The influence of the deformation parameters of medium on strength parameters and change law under different ratios of materials are studied by means of numerical examples. The results show that the equivalent method of plastic complementary energy has feasibility to determine the strength parameters of composite medium.