Abstract: The undulation effect of fiber bundles on plain weave composites causes the variety of slave material principal direction and the concentration of out-of-plane shear stress. A meso-scale finite model based on the improved voxel meshes for a unit cell was utilized to explore the influence on the mechanical properties and damage behavior for plain weave composites. In the model, the variety of slave material principal direction was defined according to the undulated curve of fiber bundles, and a shear correction factor was introduced into Hashin criterion which was used to predict the initial damage of fiber bundles to consider the effect of out-of-plane shear stress on in-plane tensile damage. The model can accurately simulate the in-plane tensile strength and damage process. The results indicate that the undulation of slave material principle direction gives rise to the decline of in-plane tensile strength for plain weave composite. The concentration of out-of-plane shear stress is the main factor leading to the failure of composites, and reduces the tensile strength significantly with the increase of shear correction factor. In addition, both the two factors have affected the damage behavior and failure mechanism of plain weave composites, which need to be expressed accurately in numerical analysis.