Abstract: The effect of inlet loadings,empty bed residence time(EBRT),drenching density and mass concentration of NH_-4Cl in the nutrition solution on the performance of the trickling biofilters,which were packed with different sizes of ceramic rasching rings and used to purify xylene in waste gas,were studied.The results of experiments show that the removal loadings increased when the inlet loadings increased.But the relationships of them were nonlinear.When the EBRT increased,the removal loading increased.The effect of the mass concentration of NH_-4Cl in the drenching liquid on the performance of the reactors is obvious,and the drenching density of solution has almost no effect on the performance of the reactor when the nitrogen source is enough.