Six horizontal subsurface-flow constructed wetlands were operated year round at a wastewater treatment plant (WWTP) in Nanjing, China, to investigate the influence of temperature on nitrogen removal, micro-environment and plant eco-physiological characteristics. The data obtained showed that the removal rates of DON, NH4+-N and TN were significantly temperature-dependent. The substrate ureases activity and microbial nitrification intensity dropped as temperature decreased. Urease activity and nitrification intensity in planted wetlands were distinctly higher than that in unplanted wetlands. DO concentration in mid- and upper-layer of the wetlands had greater seasonal variation than that in bottom-layer. The net photosynthetic rate and evaporation rate of reeds were both significantly positively correlated to temperature. Consequently, in order to obtain more consistent year round nutrient removal, it is suggested that some appropriate heat-preservation measures are used to cover the surface of the wetlands, cold resistant plants that are active year round, and enhanced aeration in mid- and upper layer should be adopted.