Abstract: Based on analyzing the hydrologic characteristics at high-velocity and acute fall water area,a set of theories for surveying water level in the water area are studied in the paper.At the same time,a system for water level observation is also developed and presented in the paper.The system and theories presented in this paper has been used in the project of Qing Cao Sha river closure.Comparing the tidal level from the method and that from tidal gauge,6-centimeter accuracy was achieved in the project,which shows that the method is right and the system is credible in the determination of water level at the special water area.