In order to find out the reason of the filamentous sludge bulking in salt-tolerant sludge during saline wastewater treatment，a lab-scale nutrient removal activated sludge system，based on the modified MUCT configuration，was used to identify the occurrence process of filamentous sludge bulking.The sludge was acclimated for a long period at 10g·L-1 salinity in the MUCT process and was observed to have plenty of filamentous organisms under low dissolved oxygen concentration condition.Different operation strategies were used to control the filamentous sludge bulking.The pollutants removal efficiencies during each control periods were compared as well.The results indicated that filamentous sludge bulking in salt-tolerant sludge occurred at a low DO concentration.Increased salinity inhibited sludge bulking quickly and efficiently.Limited filamentous sludge bulking could be maintained for a long time when ρ(DO2) was controlled at 1.0 mg·L-1 and ρ(DO1) was controlled at 2.0 mg·L-1.The value of sludge volume index (SVI) varied between 190 ml·g-1 and 210 ml·g-1.During this period，the effluent turbidity decreased significantly due to the filtering effect of filamentous bacteria.It could be an option to solve the turbidity problem of saline wastewater treatment.