Abstract: In order to obtain a flocculating microorganism with low-temperature resistance and excellent flocculation, UV mutagenesis and cultivation under low temperature (5℃) stress were used for flocculating microorganism separation. The results showed that:(1) The original flocculating strain was preliminarily identified as Bacillus cereus; (2) The screening gave the targeted mutant FM-5 with 75.35% flocculating rate with genetic stability; (3) Optimum flocculating conditions were determined as optimum dosage 0.90 mL/(50 mL), pH 7.4, coagulant aids 1.0 mL/(50 mL), and processing time 15 mins via univariate experiments (UE); the Box-Behnken response surface method (RSM) was used to acquire the optimum combination of application conditions:dosage 0.90 mL/(50 mL), pH 7.38, coagulant aids 1.04 mL/(50 mL); (4) Verification tests verified that the flocculating rate reached 97.01%, and BOD₅, COD_Cr, turbidity and chroma removal rates reached more than 97%, and the effluent quality met the GB 18918-2002 1 A standard of the Urban Sewage Treatment Plant Pollutant Discharge Standard. In conclusion, the flocculating ability of the original strains could be greatly improved via UV mutagenesis, cultivation under low temperature and a combination of UE and RSM, hence FM-5 could reduce more suspended solids in municipal sewage and achieve removal of various pollutants simultaneously in a plateau area.