Taking column foundation with undisturbed soil on loess as a research object, the site full-size water immersion static load test was carried out at Gangu substation of 750 kV Lanzhou-Tianshui-Baoji power transmission line project. The load-displacement of top foundation with water immersion was measured under uplift load combined with horizontal load and compressive load combined with horizontal load on the basis. Through the analysis on Q－S curves of test foundation, the ultimate uplift, and compressive bearing capacity of foundation were obtained. On this basis, the economic comparison between column foundation and spread foundation under the same design condition was carried out to further discuss the safety and economy of this kind of foundation. The research results could provide a theoretical basis for the optimization design and safety construction of 750 kV Lanzhou-Tianshui-Baoji power transmission line.