Abstract: A mathematic model for the coastal evolution has been established by one-line theory and the normal expressions of the"Code of Hydrology for Sea Harbour"of China,based on analysing the long-time evolution of the natural sandy coast in Hebei Province. The model is proved to be true and reasonable after verifying the measuring data in 2000 and 2006, so it can be used to simulate long-term evolution of the coastal line,and forecast the erosion condition of the natural sandy coast as well. The result.s of the study show that the erosion scope would move towards the south,and the region from Dapu River to Tazigou will become the center area of erosion by 2026,and the conclusion can also be applied to protecting the natural sandy coast.