In the construction of islands and reefs in the South China Sea, calcareous sand is an easily obtained raw material, but it also has disadvantages of being porous and fragile. To ensure the safety and stability of the construction of islands and reefs, the MICP-solidified calcareous sand samples are designed to undergo immersion tests and dry-wet cycles in seawater and pure water respectively to explore the durability of MICP-solidified calcareous sand samples in different environments and treatment methods. The results show that:(1) the MICP-solidified calcareous sand has good erosion resistance, which effectively improves with the increase of reinforcement rounds. It deteriorates the fastest in seawater dry-wet cycles and the slowest when immersed in pure water; (2) both immersion tests and dry-wet cycles can adversely affect the durability of the samples, and the degradation of the dry-wet cycles is greater; (3) when controlling variables, the durability of the samples in seawater is worse than that in pure water.