Tumor-associated macrophage (TAM) is a macrophage infiltrating around tumor cells, which can be divided into two categories including classical activated macrophages (M1) and alternately activated macrophages (M2). On the whole, it shows the phenotype of M2 macrophages that promote immune escape of tumor cells. With the in-depth study of the immune function of the body, the studies have indicated that TAM is highly malleable and can be transformed into each other with the change of tumor microenvironment. TAM plays a very important role in tumor occurrence, development, invasion and metastasis, and its classification and quantity may also be used as an index to judge the prognosis of tumors. Therefore, TAM is a feasible potential target for the treatment of cancer. This paper reviews the role of TAM in tumorigenesis and development.