The invention provides a supporting device for a rotary drilling bored pile, and belongs to the technical field of building construction. The supporting device comprises a supporting upright post, a first supporting mechanism and a second supporting mechanism, wherein the first supporting mechanism and the second supporting mechanism are both supported on the inner wall of a hole pile, and the first supporting mechanism is provided with an installation groove. The supporting device for the rotary drilling bored pile uses the first supporting mechanism and the second supporting mechanism whichare arranged up and down to correspondingly support an upper part and a lower part of a side wall of the hole pile, and positions of the first supporting mechanism and the second supporting mechanismare adjusted to support the inner wall of the hole pile so as to improve the stability and reliability of the supporting device for the rotary drilling bored pile; and the installation groove is formed in the first supporting mechanism, so that one end of the second supporting mechanism can move downwards, the other end of the second supporting mechanism is installed in the installation groove ina matched mode, the second supporting mechanism and the first supporting mechanism jointly support the lower side of the inner wall of the hole pile, the lower side of the inner wall of the hole pileis more stable, and the situation of collapse does not occur.