The invention relates to the field of simulation loading test class, particularly relates to a simulation loading device for robot joint reducer performance test, and provides a composite loading device for the robot joint reducer performance test. The composite loading device comprises a workbench base, a tested reducer module, a loading torsion bar module, a torque loading module, a loading lever module, leading screw loading modules and a hoisting bracket module. The loading shaft of the tested reducer module is connected with the elastic torsion bar of the loading torsion bar module. The elastic torsion bar is connected with the output flange of the torque loading module. The loading shaft is installed in the loading lever of the loading lever module. The two sides of the cantilever of the loading lever are provided with two sets of leading screw loading modules. The loading lever module is installed in the hoisting bracket module. Loading of toque, bending moment, axial force, torque and bending moment composite load and torque and axial force composite load of the reducer can be realized so that the loading performance is table, use is convenient and performing of the working performance test of the reducer is facilitated.