A rotary bucket mixing device is disclosed. The rotary bucket mixing device includes a main body, a rotating disk assembly, a power gear assembly and a first idler assembly. The power gear assembly receives a power to drive the rotating disk assembly to rotate and thereby rotating a mixing bucket disposed on a supporting assembly of the rotating disk assembly and mixing the contents in the mixing bucket. The first idler assembly controls a rotational speed. The rotary bucket mixing device of the present disclosure provides a better support to the mixing bucket and therefore the safety during the mixing process is enhanced.