Tunneling nanotubes (TNT) is a newly discovered connection mode between animal cells, and its formation is of great importance in physiological and pathological processes of animals and humans. The forming conditions and the promoting mechanism of TNT are not fully understood yet. It has been known that the state of cells (such as inflammatory conditions and stress reaction), molecular level (Fas ligand, cell adhesion molecules and the ligand interactions, M-Sec/TNFaip2/B94 and lipid molecules), and pathogenic infection are important for the formation of TNT. In this paper we reviewed the promoting mechanisms for TNT formation.