The invention discloses a large-diameter single-pile single-hook underwater pile overturning method. In the method, a crane ship with a main hook is adopted. The method comprises the following steps of calculating the distances between the main hook and main hoisting lugs and the distance between the main hook and the bottom of a single pile according to the inclined angle alpha between a hoistedsingle pile and the horizontal plane in the balanced state; then determining the diameters of main hoisting steel wire ropes and the diameter of an auxiliary hoisting steel wire rope according to alpha; hanging the upper ends of the two main hoisting steel wire ropes on the main hook, hanging the lower ends of the two main hoisting steel wire ropes to two main hoisting lugs of the single pile, hanging the upper end of the auxiliary steel wire rope on the main hook, and hanging the lower end of the auxiliary steel wire rope at the bottom of the single pile by virtue of a U-shaped clasp in a clamping manner; hoisting the single pile by the main hook, so that the single pile fall into water, and lowering the main hook until the pile tip at the bottom of the single pile touches the sea bottomsoil level; and continuing to lower the main hook of the crane ship so as to enable the auxiliary hoisting steel wire rope to be gradually in a released state, separating the auxiliary steel wire ropefrom the main hook, automatically separating the U-shape clasp from the bottom of the single pile, and then erecting the single pile by hoisting the main hook. The pile overturning method can effectively reduce investment of a ship device.