Background <p>Litter decomposition plays an important role in linking carbon and nutrient cycling between plant and soil in forest ecosystems. Understory vegetation and climate change shape forest environment together, which profoundly influence the process of litter decomposition. However, the specific effects and underlying mechanisms remain unclear.</p> Scope <p>We review how understory vegetation (including shrubs, vines, herbs, ferns, and mosses), climate change (including elevated atmospheric CO₂, warming, altered precipitation, nitrogen deposition, and their interactions), and their interactions influence forest litter decomposition.</p> Results <p>Understory vegetation can influence microclimatic conditions, including temperature, moisture, and solar radiation, which can significantly affect forest litter decomposition. It can also produce high-quality litter and enhance litter diversity, thus increasing the rates of mixed litter decomposition in forests. Additionally, understory vegetation modifies the community structure, composition, and diversity of soil fauna and microorganisms, which are crucial for litter decomposition. Multiple climate change factors can interact with each other and exhibit profoundly non-additive effect on forest litter decomposition. Most importantly, understory vegetation can regulate the extent to which climate change affect forest litter decomposition, increasing the unpredictability of climate change impacts on forest litter decomposition.</p> Conclusion <p>Overall, this review highlights the role of understory vegetation in regulating forest litter decomposition, and provides new implications into sustainable management practice of forest plant and soil under climate change.</p>