Abstract: By use of laterally confined compression-degradation equipment,comparative tests on simulating different degradation conditions were operated to investigate the process of biodegradation for municipal solid waste(MSW).The produced gas and leachate were collected and CODcr,BOD5,pH,CO2 and vertical displacement,etc.were measured periodically.The bioreactor cell could simulate the first three phases in landfill successfully: the original adjusted phase,the transitional phase and the acidification phase.It was shown that the volume reduction due to biodegradation(VRDB) of organic fraction of MSW gained by contrastive cases directly was 24% of the total volume.The volume reduction due to biodegradation could be expressed as the exponential function of time.It was proved that the decomposition rates and volume reductions due to biodegradation varied with reaction phases and the VRDB of acidification phase was 70% of the total reduction.