Classical Molecular Dynamics simulations were carried out to study the interaction of two zigzag graphene nanoribbons (GNRs). Remarkably, single walled armchair carbon nanotube could be formed via two zigzag GNRs at room temperature. The reaction process strongly depends on the distances between two ZGNRs and the widths of ZGNR. Our results suggest an effective route for the controllable growth of specific armchair nanotube.