Abstract: The functional role of coastal artificial islands has expanded from traditional land reclamation to comprehensive ecological enhancement. However, their construction alters local sediment dynamics, potentially significantly affecting the stability of downdrift sandy coasts. Based on sediment dynamic mechanisms, the impacts can be categorized into three types: ① Wave diffraction-dominated; ② Longshore current-blocking; ③ Tidal current-induced erosion-accretion coexistence behind islands. Five representative cases—Qinhuangdao’s Putao Island, Yantai’s Lianli Island, Zhangzhou’s Shuangyu Island, Nanhai Pearl Artificial Island and Wanning’s Riyue Island—were analyzed for their impacts on downdrift coastal stability. Findings indicate that artificial islands induce complex hydrodynamic and morpho dynamic responses, often involving multiple interacting mechanisms rather than a single mode. The development of connecting sandbars is jointly controlled by island size, offshore distance, and basal water depth, with large nearshore islands more likely to form prominent bars. Additionally, extreme events interacting with artificial islands can further modify downdrift beach morphology.