Abstract: In order to solve the problem of shortage of carbon source,the poor biological denitrification,and large production of waste activated sludge（WAS） in the urban sewage treatment plants,the effects of alkaline fermented liquid as external carbon source on biological denitrification and phosphorus removal efficiency were studied with the method of adding different ratio of alkaline fermented liquid into A 0system.The results showed that with the amount of alkaline fermented liquid additive increasing,the inflow pH value of A 0 system increased,and the COD and NH/-N removal efficiency basically remain unchanged,but the TN and PO₄^3--P removal efficiency slightly decreased.When all the external carbon source were provided by fermented liquid,COD,NH₄⁺-N,TN and PO₄^3--P removal rate were 87.00% ,98.86% ,79.93% and 80.92% respectively,and NH₄⁺-N.TN and PO₄^3--P remove quantity were improved by 24.93% 、19.05% and 86.08% respectively than single additive sodium acetate.