With the development of China's bridge and construction technology, in order to minimize the cost of the project, there are more and more projects requiring super-deep hand-dug piles under complex geological and topographical conditions, and the technical difficulty is far beyond the specification requirements, which is detrimental to the safety of the dug-hole operation. This paper describes in detail the derivation of the formula for calculating the thickness of the retaining wall, which is directly related to the construction technology and safety of super-deep hand-dug piles under complicated geological conditions, and at the same time, combines the calculation formula with the engineering examples to explain the application of the formula.