Based on the practical experience of Luotou water channel super large-crossing in 220 kV Zhoushan-mainland electric power grid project, the mechanical behavior of huge steeling plug-in foundation under difficult loading and geological conditions is analyzed by using finite element method, which considers the nonlinear properties of concrete and the interaction between foundation, anchors and rock. Under eccentric loads, the base resistance of foundation is distributed in trapezoid shapes. The eccentric stress states and uneven settlements of foundation can be improved by applying two-sided linking beams in the middle of column. The uplift loads can be effectively transferred by internal anchor plates, and the scope of cracks in concrete can be prevented by some adjustments on the reinforcements. Some attention, which must be further paid on the design of steeling plug-in foundation, has also been discussed.