Abstract: To investigate the mechanical response and failure mechanisms of 2.5D woven composites under complex in-plane loading, this study utilized finite element numerical simulations to analyze the periodic deformation characteristics of off-axis weft yarns. A more realistic parameterized unit-cell model was established, and failure envelopes of the composites under various load states were obtained through progressive damage simulation. The findings indicate that due to differences in the mechanical properties of warp and weft, the failure envelope of 2.5D woven composites under orthotropic bidirectional loading lacks symmetry observed in two-dimensional woven composites. There exists a competitive relationship between the mechanical properties of warp and weft: as weft density and warp crimp rate increase, the mechanical properties of warp are weaken, while the mechanical properties of weft improve with an increased volume fraction of weft fibers. These insights can guide the rational optimization of weaving process parameters, thereby enhancing the overall mechanical performance of 2.5D woven composites under complex service conditions.