In this paper,the concept,types and mechanism of activated sludge bulking were introduced.The factors affecting the sludge bulking were discussed from the aspects of wastewater quality,such as wastewater with high content of carbon hydrate,decayed wastewater,wastewater with toxic substance,wastewater with unbalanced content of N and P and wastewater with low pH value;the environment conditions such as flowing state of the flow,operation manner,variation of water quality and other factors(pH,temperature,nutrition) etc.And also,the emergency controlling,environment controlling and process operating controlling methods are put forward for controlling activated sludge bulking.