Constructed wetland systems are increasingly used to treat domestic sewage, industrial wastewater and agricultural runoff in recent years.The wetland treatment process has been gaining international interests and applications due to its low maintenance and operational cost, and high removal capacity.Because environment has significant effects on the purification ability of constructed wetland systems, it is very necessary to study purification effects of constructed wetland systems in different seasons.In the paper, seasonal variation of the distributions of microorganism in the root-zones of wetland plants (Phragmites australis, Zizania caduciflora, Typha latifolia etc.);the substrate layers of control SSPs, together with the effects of wastewater treatment were studied.The results are as follows: (I) the numbers of microorganisms in the different plant root-zones were different;the purification effects were also different.(II) The numbers of bacteria in the fall were higher than those in the summer for the three plant zones and the control, and the number of fungi and actinomyces in summer was much higher than that in the fall for control.(Ill) TP removal showed a higher efficiency in summer than that in fall.(IV) Significant positive correlation between total number of bacteria in the wetland plant root-zones and removal rate of BOD5 was found;while no significant correlation between root-zone microorganisms and removal rates of TP, CODcr and KN were detected.The mechanism resulting in the above results remains to be further researched.