An active control system for a rolling behavior of a high-speed train, comprising: a sensor adapted to be arranged on the train; a controller; and an output device; wherein the output device can be arranged on a joint between two adjacent carriages of the train; the output device comprises a power unit, an output unit and a casing; and the power unit and the output unit are provided inside the casing; the casing comprises a bottom plate, an annular side plate and a cover plate; the casing is further provided with a through hole which penetrates through the bottom plate and the cover plate; and the bottom plate and the cover plate can be arranged on the two adjacent carriages, respectively; the power unit comprises a motor and a speed-increasing gear set; the speed-increasing gear set comprises a main speed-increasing gear and a secondary speed-increasing gear; the motor is fixed on the bottom plate; the main speed-increasing gear is arranged on the motor and the secondary speed-increasing gear is fixed on the bottom plate; the main speed-increasing gear engages with the secondary speed-increasing gear; and the sensor and the motor are electrically connected to the controller, respectively; and the output unit comprises a rotation inertia ring, a torque transmission ring and a connecting ring which are all hollow circular rings; and the rotation inertia ring, the torque transmission ring and the connecting ring are coaxial with the through hole; the connecting ring is fixed on the bottom plate; the torque transmission ring is connected between the rotation inertia ring and the connecting ring; an outer circumference of the rotation inertia ring is provided with teeth; and the rotation inertia ring engages with the secondary speed-increasing gear through the teeth. a sensor adapted to be arranged on the train; a controller; and an output device; wherein the output device can be arranged on a joint between two adjacent carriages of the train; the output device comprises a power unit, an output unit and a casing; and the power unit and the output unit are provided inside the casing; the casing comprises a bottom plate, an annular side plate and a cover plate; the casing is further provided with a through hole which penetrates through the bottom plate and the cover plate; and the bottom plate and the cover plate can be arranged on the two adjacent carriages, respectively; the power unit comprises a motor and a speed-increasing gear set; the speed-increasing gear set comprises a main speed-increasing gear and a secondary speed-increasing gear; the motor is fixed on the bottom plate; the main speed-increasing gear is arranged on the motor and the secondary speed-increasing gear is fixed on the bottom plate; the main speed-increasing gear engages with the secondary speed-increasing gear; and the sensor and the motor are electrically connected to the controller, respectively; and the output unit comprises a rotation inertia ring, a torque transmission ring and a connecting ring which are all hollow circular rings; and the rotation inertia ring, the torque transmission ring and the connecting ring are coaxial with the through hole; the connecting ring is fixed on the bottom plate; the torque transmission ring is connected between the rotation inertia ring and the connecting ring; an outer circumference of the rotation inertia ring is provided with teeth; and the rotation inertia ring engages with the secondary speed-increasing gear through the teeth.