A hybrid continuum mechanics and molecular mechanics model is developed in this paper to predict the critical strain, stress, and buckling load of the inelastic buckling of carbon nanotubes. With the proposed model, the beamlike and shell-like buckling behavior of carbon nanotubes can be analyzed in a unified approach. The buckling solutions from the hybrid model are verified from molecular dynamics simulations via the MATERIALS STUDIO software package and from available research findings. The existence of the optimum diameter, at which the buckling load reaches its maximum, and the correlation of the diameter with the length of carbon nanotubes, as predicted by Liew (2004, “Nanomechanics of Single and Multiwalled Carbon Nanotubes,” Phys. Rev. B, 69(11), pp. 115429), are uncovered by the hybrid model. The simplicity and effectiveness of the proposed model are not only able to reveal the chiral and size-dependent buckling solutions for carbon nanotubes, but also enable a thorough understanding of the stability behavior of carbon nanotubes in potential applications.