Constructed Wetlands (CWs) have been widely used for the advanced treatment of the secondary wastewater from Waste Water Treatment Plant (WWTP). However, the pollutant, especially nitrogen, removal efficiency is greatly limited by the lack of carbon sources in the secondary effluent treatment of CWs because most Biochemical Oxygen Demand (BOD) matter has been removed in WWTP. The main pathway of carbon source supplied from CW macrophytes and its main influencing factors were reviewed in this paper. Furthermore, the universal seasonal dynamics and modes of organic matter supply quantities were established for CW macrophytes in East China. The main objective was to develop a novel strategy to stabilize the carbon-supply function of CW macrophytes for the improvement of pollutant removal efficiency and avoidance of secondary pollution in the decomposition process of macrophyte litter by the configuration of warm-season cold-season macrophyte species. The main pathway of carbon source supplied from CW macrophytes included root exudates, decomposition of under-ground biomass, and the decomposition (and leaching) of above-ground biomass. The CW macrophytes have a relatively high carbon supply for denitrification, which is closely correlated with macrophyte species and numerous environmental factors, and thus varies substantially in both time and space. As an example, Phragmites australis with a maximum above-ground biomass of 5.0 kg/m² potentially supports a nitrate removal rate of 0.57 kg N/m² in one year, which is much larger than the values estimated by the previous studies because most previous studies only accounted for the above-ground biomass and ignored other carbon-supply paths of CW macrophytes. Because of the seasonal variation of CW macrophyte carbon-supply function, the universal seasonal models of Biomass Accumulation (BA, the un-decomposed CW macrophyte biomass) and Organic Matter Supplied Quantity (OMSQ, the decomposed CW macrophyte biomass plus the root exudates) were established for representative warm-season and cold-season macrophytes species in East China, respectively. Warm-season and cold-season macrophytes showed significant seasonal complementarity characteristics in both BA and OMSQ. Therefore, the proper configuration of warm-season and cold-season macrophytes in a CW system can greatly stabilize the carbon-supply function of CW macrophytes and thus avoid the secondary pollution by the simultaneous decomposition of most macrophytes litter. The above-ground biomass harvest and return to CW after pretreatment can further improve the artificial management of the carbon-supply function and thus increase the denitrification stimulation function of CW macrophytes. In the future, the related research should be focused on (1) development of the quantitative analysis methodology of OMSQ supplied from CW macrophytes, (2) monitoring the dynamics of the OMSQ quantity and its possible regulation strategies and, (3) design of CW with the ability of supplying stable and high quantity carbon sources from itself as planted macrophytes for improving pollutant efficiency.