Abstract: Obtained from the results of annual field in Donghu Lake, the growth and population ecology of Ranunculus sceleratus L. were studied in this paper. The life history of the species was divided into six stages, i. e. seedling, jointing, branching,flowering-fruiting, withering and dormant according to the morphological features.Although the number of individuals could reach 422 per square metre, as shown by the dynamic life table, only 122 ind. m-2, would survive and flower because of the intraspecific competition. For the high rate of mortality, the shape of survival curve of the population appeared to be Deevey Ⅲ. Moreover, its seed output was extremly large, reaching 8.728×105 ind.m-2, whilst the size of the seed was rather small. All these characteristics proved that this species is a typical plant of r-strategy. In the flowering-fruiting stage, the maximum biomass (D. W.) was 596 gm-2, among which the leaves were the organ that contributing most greatly, followed by the fruits. But the ratio of D. W. to W. W. was the maximum in fruit at 0.282. Based on the annual measurement of the height of R.sceleratus and Alternanthera philoxeroides,which offered the plant mats to support the studied population, the niches of these two species had not overlapped with a reciprocal relationship. In addition, the correlation of biomass and height of R.sceleratus was also analysed and a linear relationship existed apparently.