With the foundation resistance coefficient method, it gives mechanics analysis for the new digged foundation with wing plates when loaded laterally, and offers corrected formulas by modifying the average stress on the wing plate. Then the average stress on the wing plate is not simply equal to midpoint stress, but the average value of three points, including the upper edge point, the middle point and the lower edge point on the wing plate. At last a project example is analyzed and discussed. The results show that, the new digged foundation can reduce the top horizontal displacement and bear a heavier lateral load; corrected formulas have wider applicability in power transmission projects, and can indicate the effect of the wing plates to the lateral deformation; the new digged foundation with wide-shallow wing plates can get better results than that with narrow-deep wing plates, and is recommended for power transmission projects.