Abstract: A new type of artificial reef with high strength was prepared by using slag-CaO-FGD gypsum as cementitious material and sea sand as aggregate. The effects of FGD gypsum on the compressive strength and hydration products of the new artificial reef materials were investigated by means of mechanical properties test, X-ray diffraction, thermogravimetric analysis and SEM. The results show that the addition of appropriate amount of desulfurized gypsum can significantly improve the cementitious strength of CaO activated slag cementitious materials, and promote the preferential formation of ettringite (AFt) in the hydration process. Under the optimal gypsum content, the 3 d strength can be increased by 51.4%, the 7 d strength by 35.7%, and the 28 d strength by 25.2%. The dissolution test results of heavy metal ions show that the seawater quality of the immersed samples conforms to the national first class sea water quality standard; pH detection of surface leaching solution showed that a small amount of OH^- dissolved in the surface of the artificial reef material test block at the initial stage of seawater immersion, so that the pH value of immersion solution increased from 8.0 of fresh seawater to 8.5, but returned to the normal value after 60 days; in addition, the real sea area hanging board experiment showed that the reef had good marine compatibility and a large number of aquatic organisms attached. Low-alkalinity ecological artificial fish reefs can meet the basic performance requirements of fish reefs, have broad application prospects, and provide a new way for the comprehensive utilization of slag and sea sand.