Abstarct: Carbon nanotubes (CNTs) possess extremely high stiffness, strength and resilience, and may provide the ultimate reinforcing materials for the development of nanocomposites In this study, the effective mechanical properties carbon of nanotube-reinforced composites is evaluated using a 3-D nanoscale representative volume element (RVE) baxsed on continuum mechanics and using the finite element method (FEM). The systems being investigated consist of amorphous as well as crystalline polyethylene (PE) composites with embedded zigzag single-walled CNTs. The nanotube is modeled at the atomistic scale, and the matrix deformation is analyzed by the continuum finite element method. The nanotube and polymer matrix are assumed to be bonded by van der Waals interactions at the interface. Van der Waals forces between carbon atoms in CNT and nodes in polymer matrix are simulated by using the nonlinear springs. For testifying the effect of the interface between CNT and matrix, different boundary conditions and load cases are applied on the RVE. In one case, uniform stress is imposed, on the finite element nodes at the top surface of the matrix and the results show degradation in Young’s modulus at low aspect ratios. In ther other case, uniform stress is imposed on CNT end and matrix nodes simultaneously. The results show moderate improvement in predicted properties.