The invention relates to a variable-rigidity joint, in particular to a variable-rigidity joint based on characteristics of torsional springs. The variable-rigidity joint aims at solving the defects that in the prior art, energy saved by an existing rigid joint is not enough, variable-rigidity performance cannot be ensured easily and the variable-rigidity range is small, and aims at solving the problems that in the rigidity regulation manner that the position of a fulcrum is moved based on the lever principle, energy consumption generated when the fulcrum conducts sliding friction in a groove is large, the number of required parts is large and the structural design is not reasonable. The variable-rigidity joint comprises the set of torsional springs, a slide block, a slide rail, a first output plate, a second output plate, an input plate, an input plate rotating shaft, two rollers, a set of torsional spring supports and two connection pieces. The set of torsional springs include the first torsional spring and the second torsional spring. The set of torsional spring supports include the first torsional spring support and the second torsional spring support. The first output plate, the second output plate and the input plate are all disks. The variable-rigidity joint is used for the field of robot joints.