In this experiment,the method of biofilm colonization on sand filtration(M01 and M02)sewage treatment was studied.It is showed the regular change of biofilm development under different conditions,the increment of bacteria number,the success of micro-animal kinds and population etc in the process.The rate of removal of CODcr、NH₃-N is observed.The experimental result shows biofilms can be cultivated on the surface of the biological sand filtration,and bacteria played a key role in this process.Epistylis,Vorticella,Zoothamnium,Rataria,Nemato and other microorgnisms can also be found in the system.The degradation of COD and NH₃-N on M01 can reach 90% and 70% respectively,The degradation of COD and NH₃-N on M02 can reach 60% and 20% respectively.