The hydraulic gradient at the bottom of cutoff wall in a deep overburden foundation is large, and may cause the local seepage failure near the bottom of cutoff wall, which may induce the differential settlement and crack of anti-seepage structure threatening the dam safety. In order to reduce the hydraulic gradient at the bottom of cutoff wall, a new cutoff wall of expanded base type was proposed to change the local structure type of the cutoff wall tip. The distributions of the hydraulic gradient at the bottom of cutoff wall were compared and analyzed with different types of local structure. The results show that the expanded base structure could significantly reduce the maximum hydraulic gradient at the bottom of cutoff wall and the maximum hydraulic gradient at the downstream side; the larger the radius of expanded base structure was, the smaller the maximum hydraulic gradient was. For the generalized model, when the penetration depth of cutoff wall with the conventional type was 35 m, the maximum hydraulic gradient at the bottom of cutoff wall was 0. 85, and the maximum hydraulic gradient at the downstream side was 0. 27. For the cutoff wall of expanded base type with a radius of 1. 5 m, in order to achieve the same anti-seepage effect, the penetration depth was only 23 m. It can be seen that the type of a expanded base structure was significantly superior to the conventional type. It can significantly reduce the construction quantity, the investment, and the construction period of cutoff wall.