[en] Highlights: • DFT calculations are used to propose a FE model for zigzag PNTs. • Elastic modulus of zigzag PNTs are obtained by DFT and FE approaches. • The proposed FE simulation can predict the elastic modulus of zigzagPNTs accurately. • The effects of nanotube diameter and length on the elastic modulus of zigzag PNTs are explored. • The nanotubes with larger diameters posses larger elastic modulus. In this paper, the density functional theory calculations are used to obtain the elastic properties of zigzag phosphorene nanotubes. Besides, based on the similarity between phosphorene nanotubes and a space-frame structure, a three-dimensional finite element model is proposed in which the atomic bonds are simulated by beam elements. The results of density functional theory are employed to compute the properties of the beam elements. Finally, using the proposed finite element model, the elastic modulus of the zigzag phosphorene nanotubes is computed. It is shown that phosphorene nanotubes with larger radii have larger Young's modulus. Comparing the results of finite element model with those of density functional theory, it is concluded that the proposed model can predict the elastic modulus of phosphorene nanotubes with a good accuracy.