Abstract: Immune checkpoints (ICs) are immunosuppressive molecules expressed on immune cells, which can regulate immune cells' activation. Immune checkpoint inhibitors (ICIs) which can block the interaction of immune checkpoints and their ligands, improve the cytotoxic effect of the immune system on tumor cells. Immunotherapy such as employing ICIs has gradually become a conventional therapeutic strategy for cancer treatment. However, the low response rate and the emergence of drug resistance have seriously affected the clinical efficacy of ICIs. Reactive oxygen species (ROS) are electronic reduction products of active oxygen, as well as natural by-products of cell metabolism, which can be used as regulators of intercellular signals. Tumor microenvironment (TME) is often in the state of oxidative stress (OS), which is the imbalance between oxidative system and antioxidant system. ROS can affect the interaction with its ligands by regulating the expression and activity of immune checkpoints in TME, thus affecting the anti-tumor effect of immune cells. Accumulating studies have shown that ROS could regulate tumor immune checkpoints through several pathways. Due to different types and stages of tumor, it would be clinical beneficial to understand the mechanistic link of ROS on tumor immune checkpoint, and choose appropriate ROS regulators combined with immune checkpoint inhibitors to maximize anti-tumor effects. This article reviews the common metabolic sources and characteristics of ROS, the regulatory effect and mechanism of ROS on tumor immune checkpoints and its therapeutic application.