Abstract: Red soil is highly susceptible to splash erosion under rainfall. However, conventional microbially induced calcium carbonate precipitation (MICP) tends to produce a surface-enriched CaCO3 layer in fine-grained soils, limiting its resistance to splash erosion. To improve the spatial distribution of CaCO3, aluminum chloride (AlCl3·6H2O) was introduced into the MICP process for red soil stabilization. Solution mineralization tests, microbial soil treatment tests, and laboratory rainfall splash erosion tests were conducted to evaluate mineralization behavior, soil improvement performance, and splash erosion resistance, combined with scanning electron microscopy (SEM) to investigate microstructural mechanisms. The results show that aluminum chloride lowers the solution pH and affects CaCO3 precipitation, while the MICP process remains active and crystal growth and aggregation are altered. Compared with conventional MICP, although the AlCl3-enhanced treatment slightly reduced peak penetration resistance, it increased the thickness of the cemented layer and markedly increased CaCO3 content within the 5–20 mm depth range. Moreover, it significantly decreases splash erosion weight and improves splash erosion resistance stability. These improvements are attributed to the regulation of initial pH by aluminum chloride, which suppresses rapid early-stage mineralization, weakens surface enrichment of CaCO3, and facilitates the formation of a relatively continuous and stable composite cementation structure with aluminum hydroxide colloids, thereby enhancing splash erosion resistance.