In order to shorten the constructive period and improve the working efficiency, we create a method of one-step forming under water of a varied section drilling pile. Based on the introduction of the engineering condition and technical difficulties, this paper analyzes the technical plan in detail. A new steel protecting tube is invented to realize integral pouring of pile cap and pile body under water and one-step forming of the drilling pile, which is proved to be reliable in engineering quality by the practical engineering and obtains a patent license.