In this paper, the untreated water from Yangtze River was stored. The turbidity of the water was reduced from 60 NTU to 1 NTU in the first 10 days, but the TOC value reduced only by 0.291 mg/L in 60 days. The organic molecular weight distribution and the organic polarity of storage water was analyzed using UF and XAD resin respectively. It was found that the organic matter, whose molecular weight is less than 4000 dalton, was decomposed and the hydrophilic organic matter was converted into hydrophobic organic matter.