Abstract: To study the anti-permeability of soil-cement mixing piles under special coral reef geological conditions, taking a certain foundation pit water project of Hainan Island as the background, through the penetration tests on undisturbed soils and in-situ core tests, the impermeability variation laws of bentonite cement admixtures are obtained. The results show that: (1) the soil-cement mixing piles have good applicability in waterproofing engineering under coral reef geological conditions; (2) at the early stage, the influence of cement on soil-cement permeability is greater than that of bentonite, and at later stage due to the compact effect of bentonite, the influence of bentonite on soil-cement permeability is greater than that of the cement, and with the increasing quantity of bentonite, permeability coefficient of soil-cement decreases, and anti-permeability increases gradually. It has a certain referential meaning to waterproofing engineering under coral reef geological conditions.