Abstract: Large-scale and disorderly sand excavation in the Pearl River Delta in recent 30 years has changed the evolution trend of more water and less sediment and the stable river regime,promoting the change of riverbed from slow deposition to large erosion,and the low water level has decreased significantly. This artificial effect has covered and far exceeded the natural evolution of rivers in the same period,and has a crucial impact on water intake and supply,ecological protection,shipping security and so on. On the basis of summarizing the study of water level changes in deltas and estuaries,this paper takes the Pearl River Delta network system as an example,and divides it into perennial tidal current section,seasonal tidal current section and perennial runoff section according to the change of low water level. Among them,the perennial tidal current section is basically not affected by sand excavation;the closer the seasonal tidal current section is to the low-water tidal current boundary,the greater the change of low-water level;and the lower-water level is caused by backward erosion in the perennial runoff section. Combined with the process of water and sediment variation,this paper attempts to explore the response mechanism of hydrodynamics to the rapid evolution of riverbed,in order to provide basis for navigation low water level design.