Activated sludge model 2d (ASM2d) proposed by IAWQ was modified,and it was used to simulate wastewater treatment containing biomass flocs. Combined with the operation parameters of a double-channel DE-oxidation ditch, a calculated model was built to simulate carbon,nitrogen and phosphorus degradation processes. The results showed that it could fit the experiment data well. The removal rates of pollutant in the four phases in a cycle were also calculated. And the analyses provided an insight in the nitrification,denitrification and phosphorus removal mechanisms in such operation system,which was useful for the system diagnosis and optimization.