Abstract: Based on the anisotropic damage evolution mechanisms of ceramic matrix composites under multiaxial stress, analytical model and methodology have been proposed for damage decoupling investigation, through which the interaction effects among damage components can be quantificationally characterized. Considering that the internal stresses of the load carrying material would be enhanced by mechanical damage, the parameter of effective stress was introduced in order to describe the degradation of load bearing capacity induced by micro-damage. Moreover, the maximum effective stress criterion and the quadratic effective stress criterion were suggested for strength failure discrimination under complex stress state. The damage evolution and strength failure analysis was performed with plain-weave C/SiC composites subjected to incremental cyclic tests of on-axis and off-axis tension and in-plane shear. Comparison between experimental and theoretical data demonstrates that the established strength theory is reasonable, and the predicted results are accurate.