The invention discloses an adjustable supporting device of an underwater rotary machine. The adjustable supporting device of the underwater rotary machine comprises a base, a lifting pillar and lifting piles. The lifting pillar is fixedly welded to the center of the top surface of the base. The lifting piles are fixedly welded to the four corners of the bottom surface of the base and the position close to the center of the base. The adjustable supporting device of the underwater rotary machine is convenient to use, and the requirements for firmly fixing the adjustable supporting device to the water bottom and keeping the adjustable supporting device balanced can be met by adjusting the lifting pillar and the lifting piles; the toppling force generated when the rotary machine rotates can be effectively counteracted.