Water quality, flux and temperature of polluted river in northern China fluctuate a lot in a year around, which is disadvantageous for sustainable operation of subsurface constructed wetland treating polluted river water. A pilot system of subsurface constructed wetland treating polluted river water was operated for one year to study the sustainable operation of the process. The results show that ammonia removal performance fluctuated a lot according to different seasons. At the hydraulic loading of 15 cm/d, ammonia nitrogen removal rates were above 70% in summer, however, below 30% in winter when water temperature was below 15 degrees C. Changes of water temperature had little influence on COD removal performance. In the wet season of summer, the pilot wetland system could bear a short-period flood hydraulic loading, and ammonia nitrogen and COD removal rates were 52% and 36% respectively at the hydraulic loading of 100 cm/d. The activity of soil dehydrogenase had a positive correlation with seasonal changes of temperature and pollution removal performance.