Abstract: Tumor microenvironment (TME) is the internal environment of tumor. As a functional unit, the microenvironment determines the occurrence and development of tumors. Hypoxia, inflammation and immunosuppression are three major characteristics of TME. Hypoxia signals involve in multiple immunosuppressive pathway. There is communication among the gut microbiota, chronic inflammation and immunity. The three characteristics are associated with each other to form a complex network affecting the metastasis of the tumor. TME also influences the development of immunotherapy and efficacy of drugs in solid tumor. Therefore, it is important to identify the valuable biomarkers to predict disease progression, to elucidate the mechanistic networks in the microenvironment, to develop microenvironment targeting drugs and effective drug combination strategies to improve the drug efficacy. All of these have a profound clinical value.