Abstract: The quantitative assessment of wetland water purification functions is important for wetland restoration and water environment management. Based on the literature review, the purification mechanisms of wetlands for suspended solids, organic matter and nutrients have been summarized. The types, advantages and disadvantages, and limiting factors of constructed wetlands were analyzed. The functions of constructed wetlands in purifying new pollutants and reducing greenhouse gas emissions need to be further enhanced. In addition, the quantitative assessment methods for the water purification function of natural wetlands have been summarized, and the driving factors and limiting factors of the hydrological, hydrodynamic and vegetation modules in the numerical simulation have been sorted out. Additionally, a notable contribution of this review is its focus on the advantages of assessing water purification functions from the perspective of wetland complexes within a watershed. This approach provides valuable insights for establishing appropriate pollutant concentration control thresholds, which are particularly relevant in the context of wetland ecological restoration projects, comprehensive water quality improvement efforts across entire watersheds, and the planning and implementation of water transfer projects for lake wetlands. Finally, the review proposes future research directions based on an analysis of current research trends and identified gaps in the field of wetland water purification studies. It suggests a strategic shift in focus from single wetland research to a broader watershed scale perspective that considers wetland complexes. The review also advocates for increasing the density of data monitoring in key water quality areas, establishing long-term and large-scale ecological databases, and developing integrated models of large-scale wetland complexes. These initiatives are conducive to enhancing the ecological construction level of the entire river watershed in China and the water purification capacity of wetlands.