Abstract: In recent years, with the increasing installed capacity of offshore wind power, the super-large-diameter steel pipe pile foundation has been widely applied. As the effect of soil plug weakens or disappears with the increase of the pile diameter, accurately calculating the inner frictional resistance of super-large-diameter steel pipe piles is especially important. In this study, the centrifugal model tests on the vertical bearing capacity of super-large-diameter steel pipe piles in sand are carried out using the double-wall pile form to study the inner frictional resistance. Then the action laws of the inner frictional resistance under different diameter-to-length ratios of steel pipe piles with diameter larger than 4 m are studied using the numerical simulation method. The calculated results are compared with API standard, and a new formula for calculating the inner frictional resistance is proposed. The research reveals that the inner frictional resistance of the super-large-diameter steel pipe pile shows a triangular pattern with the pile end greatly decreasing along the pile body. When the diameter-to-length ratio is less than 0.2, the inner frictional resistance of the steel pipe pile calculated by API standard is too large.