In order to study the effects of plants' roots oxygen release on the nitrification and de-nitrification in man-made wetlands, we selected two operation modes,namely traditional continuous operation mode and new operation mode (a continuous feeding during the day and stop feeding during the night).The experiment was carried out in a small integrated vertical-flow man-made wetland system with a hydraulic loading rate of 0.71 m³/(m²·d),and the representative emergent plant cattail as the wetland plant was chosen.The results showed that the aerobic nitrification took place mainly during the day and the anaerobic-anoxic de-nitrification, during the night,in the system.In addition,the daytime nitrite accumulation was 5 times and nitrate accumulation was 2 times in new operation mode comparing to those in traditional mode,the decrements of nitrite and nitrate were 64% and 26% bigger, respectively,than in traditional mode.The new operation mode showed a better nitrogen removal effect.