Taking the advantage of nanomaterials to protect the environment and avoiding the side effect need a fundamental understanding of the growth mechanism of the nanomaterials. Here, the van der Waals interaction between a nanoparticle and a nanotube in the oriented-attachment growth of nanotubes is quantitatively evaluated for the first time. In particular, the correlation between van der Waals interaction and the growth parameters is investigated in depth. Our work opens up the opportunity of studying the important interparticle interactions in the oriented attachment growth of nanotubes.