In recent years, the research on the occurrence and development process of malignant tumors and their treatment strategies has expanded to the integrated consideration of tumor tissue and tumor immune microenvironment (TIME). The TIME is composed of tumor cells, fibroblasts with their related matrix proteins, vascular endothelial cells, and immune cells, as well as a series of cytokines and chemokines, and extracellular matrix. The composition and phenotype of the TIME can affect tumor progression and response to treatment. A full understanding of each component of the TIME is helpful for the treatment decision-making and prognosis prediction. Eosinophils (EOS) are important components of TIME. They are produced from pluripotent stem cells in the bone marrow, and released into the blood as mature cells, and then migrate to tissues. This process is affected by the regulation of a variety of cytokines, chemokines and adhesion molecules, as well as by chemotaxis of a range of mediators secreted by EOS themselves, mast cells, fibroblasts and other components. Mature EOS possess primary and secondary granules that contain a range of cytotoxic basic proteins such as major basic protein (MBP), eosinophilic neurotoxin (EDN), eosinophilic cationic protein (ECP), and eosinophilic peroxidase (EPX), and can also secrete neurotrophic factors, interleukin, chemokines and other soluble components. At present, most studies on EOS focus on the analysis of the impact of EOS level on prognosis and the interaction between EOS and other components of the TIME. However, the signaling pathways and exact mechanisms associated with the pro-tumor or anti-tumor role of EOS are still unclear, and the relevant histological studies and clinical trials are also limited. So, this aspect needs to be investigated and improved further.