Abstract: Based on the geometric model of a unit cell and meso scopic computational mechanics, the present paper predicts the nonlinear behavior of constitutive relation for three dimensional multi directional braided composites. Meso scopic damage behavior is simulated by introducing Murakami's damage theory and using finite element method. Numerical examples are given and compared with experimental results. to demonstrate the nonlinear constitutive relation of four directional braided carbon/epoxy composites.