In order to study the shoal protection effect and hydrodynamic characteristics of spur-dikes under the condition of low sediment concentration,the measured topographic data of 2014 to 2021 are used to quantitative analysis the evolution characteristics around the north dikes of Qingcaosha Reservoir after the implementation of spur-dikes.The hydrodynamic and frontal incident waves' characteristics of spur-dikes are simulated under the terrain in 2014 and 2021 on the basis of the numerical model MIKE21.The results show that siltation appears in dam field shoals between 2014 and 2021,with a maximum siltation thickness of nearly 10 meters after the implementation of spur-dikes in north dikes of Qingcaosha Reservoir.The rates of erosion and siltation in shoals slow down,after the elevation of shoals reaches 0 m,they remain stable with a slope between 1:3 and 1:5.There is no scouring pits formed at the head of spur-dikes,which may be related to the fact that the elevation of the Xinqiao Channel has reached -15 m before the implementation of spur-dikes.With the sedimentation of shoals in the dam field,the tidal current velocity of the beach near the main channel is increasing.The amplitudes of tide levels and significant wave height under simulated conditions are less than 0.03 m,which is basically not affected by the siltation of the dam field.The spur-dikes has protection effects under low sediment concentration,which can be used to build the foundation of beach protection projects for the Yangtze River Estuary's water flow erosion embankments.