Abstract: In order to effectively implement the concept of green construction of transmission lines advocated by State Grid Corporation of China, this paper introduces the practical problems faced by undisturbed soil excavation foundation, compares the economy of rigid step foundation and flexible plate column foundation under critical conditions, and puts forward the view that rigid step foundation is indispensable in the foundation of 35 ~ 110kV transmission line straight tower. According to the relevant grading regulations of civil engineering specialty and decades of on-site construction experience, it is suggested that the operation margin and grading should be cancelled after removing the surface soil with a thickness of about 1.0 m for the foundation pit within 3.0 m of loose sand and gravel pit. The full-filling construction technology is adopted for the rigid step foundation slab, which reduces the excavation of earth and stone, the amount of foundation concrete, steel bar and the process of supporting formwork, greatly improves the foundation pull-out force or reduces the depth of foundation pit, and effectively solves the terrain limitation of mechanical excavation of undisturbed soil excavation foundation and the artificial excavation dilemma of embedded foundation in strongly weathered rock stratum.