Calcium carbonate sand is mineralized from the remains of marine organisms such as shells and coral reefs, and is formed through long-term sedimentation. This article studies the elemental composition and mineral structure of shells, calcium carbonate sand, and coral reefs using an X-ray fluorescence spectrometer and an X-ray diffractometer, respectively. The results show that Ca, Sr, Mg, Al, and S elements are common to shells, calcium carbonate sand, and coral reefs, among which the shell has a higher Ca content compared to calcium carbonate sand and coral reefs, and the lowest content of Sr and Mg elements. The main components of shells, calcium carbonate sand, and coral reefs are calcite and aragonite calcium carbonate, with a small amount of magnesian calcite found in the test samples of calcium carbonate sand and coral reefs. This study reveals the basic characteristics of different carbonate sediments in the South China Sea area, providing data support for the optimization of coral sand engineering.