To evaluate the effect of aerated grit and degreasing tank(AGDT) with long hydraulic retention time (>10 min) on nutrient and phosphorous removal performance at municipal wastewater treatment plant(WWTP), influent characteristics, effluent quality, removal efficiencies, activated sludge characteristics and composition, as well as performance assessment based on mass balance evaluation, were investigated in a full-scale WWTP. The experimental results showed that: Compared with Pista grid pre-treatment, AGDT pre-treatment was unsuitable to be used in WWTP with low C／N rate wastewater because it consumed more carbon source and led to decrease of effluent COD／TN／TP rates; The total nitrogen(TN) removal efficiency and total phosphorus (TP) removal efficiency decreased 5.87％ and 10.22％; The activated sludge characteristics and composition were changed with TN content increased and TP content reduced; Mass balance evaluation approach also showed that the available carbon source was decreased in secondary biochemical treatment after AGDT pre-treatment. Therefore, the effect of AGDT with long hydraulic retention time (>10 min) on full-scale WWTP nutrient and phosphorous removal performance was negative.