The higher the water environment quality in a river was, the higher self-purification by sediment micro organisms was. Restoring system of the self-purification in the river was composed of forests and heavy rain. The forests supply water, micro organisms and moderate nutritive substances to the river, and retain the self-purification power. Heavy rain cleans dirty sediment and dirty water in the river, and improves the water environment. In the seasons when we have little rain, such as late autumn and winter, its water environment and the species of micro organisms there become like those of sewage in the local points of the river where a large quantity of domestic and industrial waste water flows in. In the other hand, the worse the water environment quality in the polluted sea area was, the higher the self-purification was. However, the better the water environment quality in the clean sea area was, the higher the self-purification power was.