Based on the difference between the mechanical properties of coral reef sand and ordinary river sand, the mechanical properties and microstructure of concrete prepared with the two types of sand were investigated. The experimental results show that, coral reef sand exhibits loose structure with open pores, multi edges and fragile. Compared to the ordinary river sand concrete, the compressive strength of coral reef sand concrete mixing with sea water develops rapidly, but the growth rate is relatively lower. The elastic modulus is lower than that of the ordinary river sand concrete. The flexural strength and splitting tensile strength of concrete are almost the same as those of the ordinary river sand concrete. The hydration products of coral reef sand concrete and ordinary river sand concrete mixing with sea water are similar. The hydration products and the pore surface of coral reef sand are tightly combined.