Abstract: The present invention discloses a stiffness-variable joint actuator with motor-reducer integration, and belongs to the field of robots. The stiffness-variable joint actuator includes: a torque motor, which includes a casing, a stator, a rotor, pin gears, and pin gear rollers; and a reducer core, which includes cycloidal gears, a planetary carrier, and an eccentric shaft. The motor is connected to a cycloidal-pin gear reducer, thereby achieving the technical effect of enhancing the impact resistance and reverse actuation capability of the actuator. The rotor is disposed outside the stator, the eccentric shaft is connected to the rotor, and the reducer is disposed inside the motor, thereby achieving the technical effect of integrating the motor and the reducer and reducing the axial dimension of the actuator.