Based on the ultimate load test of the national power grid of 500kV transmission line project from Luping to Fule, this paper carried out the ultimate load test of 3 rock-socketed piles with enlarged base. The load-displacement curves, distribution of axial force of pile shaft and shaft resistance were investigated. Results show that, when the piles located in the same layer of rock-soil and the length are reached, the enlarge base pile can not only increase the ultimate uplift bearing capacity, but also reduce the displacement of pile top than the pile of uniform section. The properties of the rock mass of the enlarged head have great influence on the uplift force. For the rock socketed uplift pile with enlarged bottom, the uplift force of the enlarged head is higher than that of the ultimate uplift load of the pile, and the expansion action of the enlarged head is more significant. The uplift pile of a clay layer with a certain thickness and a strong weathered layer in a medium weathered layer with enlarged head and a uniform section at the upper end of the enlarged head, the limit side friction of the section with the clay layer and the strong weathered rock layer can be improved appropriately according to the actual situation of the project on the basis of the recommended by the building codes.