Anisotropic constitutive theory of ceramic matrix composites (CMCs) is necessary in thermal structure design and thermomechanical performance evaluation, and it is required further development. To predict the nonlinear stress-strain behavior of CMCs subjected to macroscopic plane stress state, a mechanism-based damage constitutive framework was suggested based on the conception of continuum damage mechanics (CDM). The constitutive model was formulated through two methods, i.e., total strain partitioning into elastic and inelastic strains and damage decoupling characterization. Description of damage evolution considered both the interactions among damage components and the damage intensification/deactivation effects induced by stress components. In order to evaluate the applicability, the theoretical model was utilized toward a typical plain-weave CMC, i.e., 2D-C/SiC, which usually presents nonlinear mechanical behavior. The stress-strain correlation, stiffness variation, as well as damage evolution law under different incremental cyclic loadings, i.e., tension, compression, and in-plane shear, along both on-axis and off-axis orientations were comprehensively presented in terms of experimental data and analytical modeling results. The reasonability and accuracy of the constitutive model was then illustrated as the theoretical predictions and experimental results were in good accordance with each other. This ensures the feasibility of the theoretical model in the field of CMCs, so that it is recommended to be selected for predicting the nonlinear constitutive behavior.