In order to investigate the effect of temperature on activated sludge systems,sludge settleability,nitrogen and phosphorus removal processes were investigated by changing temperature variation patterns using 4 sequencing batch reactors(SBR).The results showed that no matter temperature changes in the range of 15-22 ℃ (decrease or increase)gradually or sharply,it has little effect on nitrogen and phosphorus removal processes.But when temperature decreases to 12 ℃,biochemical reactions will be inhibitted obviously.At least 1 sludge retention time(SRT)is needed for nitrification adapt to new temperature envirionment,and more time is necessary for phosphorus removal process.When temperature increases from 12 ℃ to 22 ℃ sharply,nitrification process deteriorates seriously,but phosphorus removal process shows no change.In addition,sludge settleability deteriorates when temperature changes sharply(decrease or increase),but the reasons are different.Under temperature decrease condition,it is mainly caused by the increase of accumulated extracellular polymeric substances(EPS).Under temperature increase condition,the loosing sludge fiocs' configuration is the main reason.It should be pointed out that the filamentous bacteria content during the entire experiment keeps almost constant,and the sludge settleability variations are the reflection of the change of sludge physicochemical characteristics.