Since the concept of a type 3 secretion system was proposed, the study of related molecular mechanisms has furthered our understanding of it. In contrast to the signal peptide in other secretory machineries, there is no conserved signal sequence when the protein is secreted or transported through the bacterial type 3 secretion system. A variety of secretory signals that guide the secretion of type 3 secreted protein have been discovered in the recent study. This article introduces the categories of bacterial type 3 secretion system, the types of secreted proteins in the secretory system and focuses on molecular characters of secretion signals, providing new ideas for the development of new antibacterial drugs.