Utilizing a combined velocityvariable biofilter，a fullscale experiment was carried out on advanced treatment of secondary effluent from an oxidation ditch wastewater plant．The study was made on the performance of the biofilter at three different hydraulic loadings．The results showed that the highest average removal rate of CODcr reached 21.42%,which increased with hydraulic loadings rise; the highest of those of NH3N and turbidity was 43.19% and 60.40%.respectively.The study shows that this biofilter technology is an good process for advanced treatment of secondary effluent which is characterized by deficiency of nutrition and low biodegradability．