Abstract: According to the characteristics of a buried sewage treatment system,the start-up of high concentration microbial agents in dealing with analog household sewage was studied in a biofilm reactor.When the chemical oxygen demand,ammonia nitrogen,and total phosphorus are 750,48 and 7.5 mg·L^-1,the removal rates of them are 85%,58%, and 35% after operation for 10 d,respectively.Optical microscopy and environmental scanning electron microscopy observations show that with the system removal rate increasing,the microbial species gradually changes.The results of polymerase chain reaction-denature gradient gel electrophoresis(PCR-DGGE) demonstrate that the microbial species on volcanic rocks and suspended fillers are abundant,and the microbial community changes under different conditions, but the whole system of microorganisms maintains relatively stable.