Abstract: An ecological wastewater purifying project consisting of three ponds with Eichhornia crassipes growing therein connected in tandem was constructed for in-depth purifying tail water from a town-run sewage treatment plant. Greenhouse gases (CO₂, CH₄ and N₂O) emitted in the operation of the project were collected and analyzed with a home-developed in-situ bubble trapping device coupled with gas chromatography during the period of August-November, 2015 to explore characteristics of the emission and relationship of the emission with the main environmental factors of the waterbody. Results show that the ecological project performed quite well in removing TN and TP with a rate up to 68.07% and 64.21%, respectively. The concentration of TN in the effluent of the project approached to the criteria of Grade V of the "Standard for Environmental Quality of Surface Water (GB 3838-2002)" and the concentration of TP was lower than the criteria. During the study period from August to November in 2015, the average flux of CO₂, CH₄ and N₂O emitted from the project was 0.058, 0.076 and 1.539 mg·m^-2·h^-1, respectively, and the cumulative emission of CO₂, CH₄ and N₂O reached 1.273, 1.685 and 33.59 kg, respectively. The fluxes of CO₂ and CH₄ varied significantly with the season, being much higher in summer than in autumn, whereas the flux of N₂O did not. Along the direction against the water flow in the ecological project, the fluxes of CO₂, CH₄ and N₂O increased first and then declined. Correlation analysis shows that the fluxes of CO₂ and CH₄ were closely and positively related (P<0.05) to the temperature of water in the ponds; the flux of CO₂ was significantly and negatively related (P<0.05) to pH and DO; the flux of CH₄ was negatively related (P>0.05) to pH and DO; and the flux of N₂O was positively related (P>0.05) to TN and NO₃^--N concentrations in the water. All the findings in this study may serve as a useful reference for evaluation of greenhouse gases emission from ecological wastewater treatment projects of ponds grown with Eichhornia crassipes.