The type VI secretion system (T6SS) is a nanoscale contractile device, which is widely found in the gram negative bacteria. This machine can kill eukaryotic predators or prokaryotic competitors by injecting toxic effectors into target cells. In the past decades, the diversity of T6SS gene clusters, the assembly of the T6SS, and the infection mechanism of the effectors have been investigated extendedly, making great progress. This review summarizes the knowledge of the T6SS from four aspects, including the composition and diversity of the T6SS gene clusters, the structure and assembly of the T6SS machine, the type of the effector, as well as the regulation network to provide insights for further T6SS research.