Objective：To investigate the activation of monocytes（THP-1）by exogenous interleukin 18（IL-18）and the proliferation，metastasis and invasion of lung cancer A549 cells by THP-1 induced by IL-18 activation influences. Methods：The role of tumor associated macrophages（TAMs）in tumor microenvironment in vivo was simulated by IL-18 induced THP-1 in vitro. The chemotactic effect of IL-18 on mononuclear cell THP-1 was detected by Transwell method. Exogenous IL-18 stimulated THP-1 cells and detected the proportion of M1 and M2 TAMs；IL-18-activated TAMs and lung cancer cells A549 were co-cultured. The changes of proliferation，migration and invasion of co-cultured A549 cells were detected by cloning experiment，cell scratch test and cell invasion assay. The morphology of A549 cells after co-culture was observed by scanning electron microscope. The expressions of epithelial mesenchymal transition（EMT）marker proteins E-cadherin，N-cadherin，Snail and Slug in A549 cells were detected by qRT-PCR and Western blot. Results：IL-18 had a significant chemotactic effect on THP-1 cells. Exogenous IL-18 stimulated the THP-1 cell phenotype from M2 to TAMs. IL-18 induced THP-1 promoted the proliferation，migration and invasion of A549. Scanning electron microscopy showed that THP-1 promoted the growth of pseudopod of A549 cells. At the same time，the expression of E-cadherin was inhibited，and the expression of N-cadherin，Snail and Slug was promoted，indicating that IL-18 induced THP-1 activated EMT in A549 cells. Conclusion：In lung cancer，IL-18 can activate THP-1 and promote their activation. Activated THP-1 promotes the proliferation，migration and invasion of lung cancer A549 cells by activating EMT.