Variation of CH4,CO2,and O2 concentrations in layers of different depths in semi-aerobic and anaerobic landfills was analyzed over a period of 5 years.The results showed that most of the municipal solid waste became basically stable after 5 years of landfill disposal.In the upper and middle layer,the concentration of CH4 in the semi-aerobic landfill was significantly lower than that in the anaerobic landfill in different landfill periods,while in the lower layer,there was little difference in the CH4 concentration between the semi-aerobic and anaerobic landfills.The average concentration of CH4 and CO2 in the anaerobic landfill was always higher than that in the semi-aerobic landfill,while the O2 concentration showed an opposite variation in different landfill periods.This was related to the aerobic reaction of landfill waste around the perforated pipe in the semi-aerobic landfill,which inhibited effective landfill gas generation.