Antibacterial peptide is an important part of the body’s natural immunity, LL-37 is the only  Cathelicidin antimicrobial peptide found in human body, its precursor peptide hCAP-18 mainly released by neutrophils. It is cut by serine protease 3 in order to produce active LL-37. The expression and activity of LL-37 was influenced by various factors in vivo and in vitro. Except for direct bactericidal function, LL-37 also regulate the release of immune and inflammatory mediators, causing immune cell differentiation and chemo taxis, wound healing, cytokines and histidine release, and end toxin and anti-tumor. The direct bactericidal effect of LL-37 is not its most important immune mode, however, others are the main way for LL-37 involved in the immune response.