Toll-like receptors in innate immune system are of type I membrane glycoproteins. The extracellular domains contain varying numbers of leucine-rich-repeat (LRR) motifs and cytoplasmic signaling domains are homologous to those of interleukin 1 receptors. TLRs can identify the intrusion of foreign bodies in the body. Moreover, in the innate immune system the immune cell response could be activated by TLRs. This paper focused on the research progress of TLRs, ligands, activatory mechanism of TLRs and their targeted drugs.