The invention discloses a tool and method for measuring the height of the semicircular plate of a leg chord, and belongs to the field of ocean engineering equipment. The measuring tool includes a standard plate and a measuring module connected with the standard plate; the standard plate has a straight side, the straight side of the standard plate is provided with an opening groove which can hold the semicircular plate; the measuring module comprises a first base and a second base which are fixedly disposed on a side of the standard plate, a first base frame, a support rod hinged to the middle of the first base frame, a support sleeve and a right-angle scale plate in threaded connection to the support rod and movably connected to the second base; one end of the base frame is hinged to the first base; a first slide block is disposed on the sidewall of a first slot at the other end of the first base frame; the right-angle scale plate is located in the first slot and is provided with a chute for the first slide block to slide, and the hypotenuse of the right-angle scale plate is provided with scale values equal to the height value of the hypotenuse. The tool may accurately measure the height of the semicircular plate.