In this study, the surface flow constructed wetlands were set up to explore the efficiency of different benthic fauna on nitrogen and phosphorus removal in the constructed wetland system during summer and winter. The water purification mechanism was investigated by the changes of nitrogen and phosphorus contents and microbial abundance in different media before and after the operation period. The results showed that the addition of mussel and viviparidae in summer enhanced the NO3
-N and TN removal efficiency. Compared with the control group, the average NO3
-N removal efficiency increased 37.19% and 22.98% by adding mussel and viviparidae, respectively. In addition, the addition of chironomid larvae in winter made the average removal efficiency of NO3
-N, TN and TP increase by 29.51%, 15.16% and 37.62%, respectively. However, the mussels and viviparidae did not have significant effects due to the semi-hibernation and reduced metabolism of benthic animals in winter. These results indicated that the addition of benthic fauna can enhance the purification effect in surface flow constructed wetland. When suitable combination of benthic fauna was selected, the water purification effect in constructed wetland may be improved throughout the year. The results of mechanism study showed that benthic fauna promoted nitrogen removal by enhancing microbial nitrification and denitrification, plant nitrogen uptake and substrate nitrogen adsorption. The removal of phosphorus was achieved by enhancing substrate phosphorus adsorption and precipitation as well as plant phosphorus uptake. These results could provide a theoretical basis and reasonable reference for the application of benthic fauna in surface flow constructed wetlands.