The invention discloses a merry-go-round base plate adjusting device, comprising a lower platform outrigger, a clamping key unit, a lock nut, a stand column fixing shaft and a boom component, wherein the lower platform outrigger is installed at the bottom of the stand column fixing shaft, the clamping key unit is fixedly installed on the stand column fixing shaft above the lower platform outrigger, the clamping key unit comprises a clamping key, a clamping key sleeve and a shaft retaining ring, the clamping key sleeve is installed at the outer portion of the clamping key, the shaft retaining ring is installed above the clamping key sleeve, and the boom component is installed above the stand column fixing shaft by the lock nut. According to the merry-go-round base plate adjusting device, the boom component is fixedly installed by the lock nut, errors existing in the manufacture process is made up through adjusting the lock nut, and thereby the turn plate is balanced, and the problem that the turn plate surface waggles after the boom component is installed by welding.