Abstract: Two methods of coagulation and adsorption were used to pretreat a simulated micro-polluted ground water to study the relationship between ultrafiltration (UF) membrane and pollution levels of different water samples and analyze the effect of particles characteristics on flux decline. The experimental results indicate that powdered activated carbon could reduce the concentration of organics effectively, but the effect of wiping out turbidity is not obvious. Coagulation could reduce the turbidity of water effectively although it has low efficiency on organics removal. The coagulation pretreatment could improve the flux of raw water, but the adsorption has no influence on flux. The correlation fitting results of fouling index of turbidity and dissolved organic matter (DOC) show that fouling index of UF has an obvious correlation with turbidity, but no obvious correlation could be found with DOC concentration. The turbidity-causing pollutants are the major foulant under experimental condition. The colloidal and particles sized between 0.01μm and 1.2μm are the main pollutant which lead to flux decline, meanwhile, it is cumulatively on fouling index for turbidity-causing pollutants during UF process.