The invention provides a submersible drill for construction of deep water pier foundations. A hydraulic power chamber is arranged on a drill stand, the hydraulic power chamber is connected with transverse supporting devices, and drives the transverse supporting devices to extract and retract in the radial direction, and the transverse supporting devices support a well wall or the inner wall of a steel casing when extending; a main rotating-driving motor is arranged on the drill stand, and the main rotating-driving motor is connected with a cutting disc, and drives the cutting disk to rotate; and a vertical pushing device is further arranged, the vertical pushing device is connected with the cutting disc, and drives the cutting disc to lift. According to the submersible drill for construction of the deep water pier foundations, through adopting the structure, the power devices dive along with the cutting disc, fixation can be achieved through automatic supporting on surrounding rock or the inner walls of the steel casing, and drilling of automatic rock cutting can be achieved; and a construction platform on the ground is not needed to provide torque, thus construction is not influenced by change of a water level, and the submersible drill for construction of deep water pier foundations can be applied to drilling construction achieving a large diameter.