Abstract: Using homogenization and unit cell finite element method (FEM), 3D material constitutive model of twill-weave carbon fabric/epoxy composites was studied and applied on the light-weight structure of electric vehicles (EV). The micro-geometric structure parameters were obtained by observing the internal microstructure of twill-weave T300 carbon fabric/epoxy composites with the help of optical microscope, then the geometric and FEM of representative volume element of composites laminate were established; The material parameters of 3D material constitutive model was studied using the cell FEM based on the laminate theory, and the predicted values were compared with uniaxial tension and three point bending test values. Through the second development, the 3D material parameters were used on the light-weight electric vehicle structure design, the EV safety was inspected according to federal motor vehicle safety standard (FMVSS571.216). The result indicates that 3D material constitutive model developed is in agreement with tension and bending experiment results, whose relative errors are 4.04% and 7.79%. The weight of EV developed by using the twill-weave carbon fabric/epoxy composites is 12% lighter than that of the traditional vehicle under the same safety condition.