The invention discloses a rotational joint module of a modularized reconfigurable robot. On the basis of planetary reduction, one level of harmonic reduction is added on motor output, a reduction ratio is improved, an output torque is added, and the transmission precision of the module is improved. An upper end cover and a lower end cover serve as installation joints, the flange-type design with locating seam allowances and pin holes is adopted, and the module is accurately and conveniently connected and located. All electric wires are arranged in a cage-type support, the upper end cover and the lower end cover and are isolated and protected by an outer cover, thereby avoiding the problem that the electric wires are coiled when a robot moves. Mechanical limit and electric limit are arranged in the module. On the basis of adopting an incremental coded disc, a rotating potentiometer is added to measure the assistant position of module movement, absolute position information is recorded under the condition of accidental power failure, and the system can continuously work after being electrified. The rotational joint module has the advantages of reasonable and simple structure, high precision and inner routing, is convenient to install and position and is safe and reliable to use.