Abstract: The abundance of substrate microorganisms in subsurface horizontal-flow constructed wetland with different plants and without plants was monitored by plate counting and dilution methods.The results showed that the abundance of microorganisms in substrates with different plants was not obviously different and it was also the same trend in substrates with plants and without plants.The microorganism abundance of substrate in different spaces in constructed wetlands was varied and that of the top was more than that of the bottom.Under stable operation conditions,biotic community with relatively stable microorganism biomass and microbial activity was gradually developed in wetland substrate.The correlation of substrate microorganism abundances and their wastewater purification effects was studied.Analysis showed a fairly strong relationship between the abundance of microorganism in constructed wetland substrate and removal rates of BOD₅ and TN of the wastewater,indicating that the biodegradation of microorganism probably is the main way for their removal;the abundance of microorganism was not interrelated markedly to reduction of TP.Ammonia oxidation rate of soil samples in constructed wetland was also tested.The results showed that nitrification ability was interrelated markedly to the abundance of nitrosomonas in constructed wetland.