In this paper, a more refined pressure distribution expression is derived to describe the van der Waals (vdW) interaction between any two tubes of a multiwalled carbon nanotube (MWCNT). Based on this new vdW force expression, a continuum cylindrical shell model is established for the buckling and post-buckling analysis of MWCNTs. The buckling and post-buckling responses are simulated for MWCNTs with various sizes to examine the consequences of ignoring the nonlinear term in the Taylor expansion of vdW force function. By comparing the results furnished by the commonly used linear vdW force model and the present nonlinear vdW force model, it is found that the buckling responses before the critical buckling strain are almost the same. Thus, the simple linear vdW force model suffices for the calculation of buckling loads. However, the post-buckling responses simulated from present nonlinear vdW force model are significantly lower than those given by the linear vdW force model. This indicates that the present nonlinear vdW force model must be used when considering the post-buckling responses.