Abstract: Reactive oxygen species (ROS) is defined as the electron reduction product of oxygen with high reactivity which can maintain normal physiological functions and redox homeostasis. The tumor microenvironment is in a state of oxidative stress. ROS can affect multiple processes of tumor immune response by modulating the phenotype and functions of tumor cells and immune cells. With the rapid development of immunology, ROS-based tumor immunomodulation has been widely concerned and studied. In this review, the mechanism of ROS participating in tumor immune response is elaborated. Meanwhile, the research process and application of ROS in tumor immunomodulation in recent years are reviewed and analyzed.