Abstract: Natural wetlands in the Qinghai-Tibet Plateau have many important ecological functions, among which water purification is one of the important functions. However, its high altitude, hypoxia and other special natural environment and human activities may affect water quality and water purification capacity of plateau wetlands. In this study, in order to reveal water environment characteristics and the water purification capacities of plateau natural wetlands under different pollution sources, water samples were collected in Lhalu Wetland and associated channels and Chabalang Wetland in August 2020 (summer) and April 2021 (spring), and then analyzed for total nitrogen (TN), ammonia nitrogen (NH₃-N), nitrate nitrogen (NO₃-N), total phosphorus (TP), dissolved reactive phosphorus (SRP), and permanganate index (COD_Mn). The results showed that TN and NO₃-N concentrations in water were lower in summer than those in spring, but TP, SRP and COD_Mn were generally higher than those in spring. The channels connected with Lhalu Wetland were polluted by human activities in Lhasa city. The water quality in the channels was poor, especially near the Lhalu Wetland inlet and downstream channel. Lhalu Wetland effectively removed the pollutants from the upstream channels. The influent quality of Chabalang Wetland was mainly affected by COD_Mn, which might be related to non-point source pollution from surrounding agricultural activities. The effluent quality also improved owing to purification of Chabalang Wetland.The removal effect of pollutants from influent water varied in different seasons. In summer, the maximum removal rates of TN, NH₃-N, NO₃-N, TP, and SRP were 75.0%, 65.2%, 89.5%, 82.2% and 35.3%, respectively. The removal rates of TN, NH₃-N, NO₃-N, TP and SRP in Chabalang Wetland were 60.7%, 73.5%, 12.7%, 35.9% and 5.0%, respectively. No removal effect on COD_Mn was observed in the two wetlands in summer. In spring, the maximum removal rates of TN, NH₃-N, NO₃-N, TP, SRP and COD_Mn were 35.2%, 65.9%, 56.8%, 59.5%, 62.3% and 17.9%, respectively. The water purification effect of Chabalang Wetland was poor, and the removal rates of TN, NH₃-N, NO₃-N, TP, SRP and COD_Mn were 2.2%, 10.2%, 11.3%, 11.3%, 9.0% and 26.0%, respectively. The purification effects in the Lhalu Wetland and Chabalang Wetland on the pollutants were different. Lhalu Wetland had a higher removal rate of nitrogen and phosphorus pollutants, and the removal effect in summer was generally better than that in spring. As for COD_Mn, its removal rates in the two wetlands were low in spring, while no purification effect of COD_Mn was found in summer.Plateau wetlands play an important role on removing pollutants from surrounding human activities. Water quality, water level, season, wetland vegetation, wetland structure, and hydrodynamic characteristics may affect the water purification capacity of plateau wetland. Rich aquatic plant communities, low water temperature, different hydrological conditions and other factors may weaken the purification effect of pollutants in plateau wetlands. Therefore, it is necessary to regulate the inflow of wetland reasonably in order to give full play to the water purification function of plateau natural wetland.