The orthotropic mechanical behaviors of weft-knitted flax fiber fabric reinforced polypropylene (PP) composites, which were produced by hot pressing of knit layers composed of a commingled yarn with a flax fiber content of 50vol.%, are investigated in both meso- and macro-scales. In meso-scale, the repeating unit cell (RUC) finite element (FE) model is developed, in which impregnated yarns are assumed to be isotropic elastic while the matrix is modeled as an elastoplastic, isotropic solid. Then, stress-strain curves of the RUC are simulated for its elastoplastic orthotropic parameters. Finally, in macro-scale of its specimen, the tensile behavior of the composite laminates with six parallel plies is simulated by means of 3D elastoplastic FE method. The applicability and limitation of this model have been discussed.