In order to find the release rule of CH_4 during waste leachate treatment process, the discharge flux, disolved concentration, total release amount per year, discharge coefficient and influence factors in a leachate treatment plant are studied by in-site monitoring and laboratory analysis. The results show that CH_4 originates mainly from anaerobic tank with percentage of 96.8%. The release flux of CH_4 in aerobic tank correlates significantly with the concentrations of dissolved oxygen and that of CH_4 in regulating tank correlates with water temperature significantly, while pH value, dissolved oxygen, and concentrations of nitrate and nitrite are not the main factors influenced the cumulative release amount of CH_4. The average release coefficient per capita and discharge coefficient of CH_4 are detected to be 872.604~1 387.858 g/(person·a) and 9.467~15.057 g/L respectively, which are both higher than those of report produced by Intergovernmental Panel on Climate Change (IPCC). Therefore, this research is practical and social significant to provide basic data of greenhouse gas emission and promote energy saving, emission reduction as well as the clean development mechanism (CDM) project exploitation.