Treatment of printing and dyeing wastewater by anaerobic baff led reactor in a pilot plant has been studied.As the influent pH is 10.0, MLSS 20 g/ L, and HRT 9 ～ 10 h, the removal rates of COD could reach average 36.8 %, and the BOD/COD ratio of influent to ef fluent could increase f rom 0.285 to 0.447, and the biodegradability of w astew ater is improved obviously.As a pret reatment method before aerobic biological treatment of printing and dyeing wastewater, anaerobic baf fled reactor is feasible both technically and economically.