Abstract: The original functions of river dyke were mainly to prevent flood and to vie with river for land. Its deriving effects include raising water level and current velocity, delaying of cutting current from tributary to main river, squandering water resources and causing their shortage, breaking off process of naturally-recovering land fertility, destroying mechanism of naturally-washing-off salt and alkali in the surface of land, accelerating progress of land desertification, changing the structure of drainage area and destroying the environmental function of river. Constructing dyke to prevent flood and occupy river's survival space, however, caused decrease of environmental quality and even led to environmental deterioration. Human should draw a bitter lesson from it.