This paper lays particular emphasis on the analysis ofhow the structure of the downflow wastewater distributors in an anaerobicfluidised bed(AFB)affect the visible fluiclization performance of theAFB.Based on this and the study of the maximum useful volume efficiencyand minimum return flow rate in AFB,the optimum structure of downflowwastewater distributors,which meets all of the needs of performance,and the range of control velocity of the sprayhead are eventually obtained.