The interfacial mechanical behavior between Carbon Nanotubes (CNT) and composite matrices has great influence on the mechanical properties of composites, so numerical simulations based on finite element methods were presented to investigate the interfacial debonding, shear stress distributions and pullout forces of Single-walled Carbon Nanotube (SWCNT) reinforced polymer composites. An axisymmetric three-cylinder model was presented, and a cohesive model was applied to simulation of the interfacial layer between the SWCNTs and polymer matrix. The influence of the aspect ratio of SWCNTs, interfacial strength and the residual stress induced by Thermal Expansion Coefficient (TEC) mismatch on the interfacial shear stress and debonding were discussed. The results of numerical simulations show that the aspect ratio of SWCNTs, interfacial strength and the residual stress have great influence on the interfacial shear stress and debonding when the length of SWCNT is 50—100 nm, the interfacial strength is 50—100 MPa and the reduction of environmental temperature is 100℃.