Abstract: Aiming at the durability and long-term stability problems of calcareous sand-cemented soil composite foundation in the marine environment, the seawater is used as the corrosive medium to perform an indoor soaking test on the calcareous sand cemented soil, and the micro cone penetration, scanning electron microscopy, energy dispersive spectrometer, and X-ray diffraction tests are conducted to analyze the strength and microstructure characteristics of calcareous sand cemented soil with different curing time and cement ratios under seawater environment. The results show that the erosion depth of calcareous sand-cemented soil gradually increases with the increase of curing time and gradually decreases with the increase of cement ratio, and the increase of cement ratio can effectively inhibit the erosion depth of cemented soil caused by seawater corrosive ions. Compared with those of the non-eroded layer, the porosities of microstructure are lager and the Ca contents are less in the eroded layer, and the Ca content and the strength of cemented soil show a similar rule. Under seawater environmental conditions, the strength change of cemented soil is the common result of the effects of growth and erosion. In this process, the cemented soil is prone to the phenomenon of Ca dissolution, which finally leads to the strength reduction of cemented soil.