The utility model discloses a hydraulic control stepless amplitude modulation device of a vibratory roller. The hydraulic control stepless amplitude modulation device comprises a box body and further comprises a fixed inner gear ring, a first planet gear, a planet carrier, a vibrating motor, an inner gear shaft, a hydraulic control gear, an amplitude modulation motor, an outer eccentric block, an inner eccentric block, a second planet gear, an outer gear ring and an outer gear shaft. Pressure oil produced by a hydraulic system drives the amplitude modulation motor to rotate and enables the hydraulic control gear to synchronously rotate, the outer gear ring and the second planet gear drive the outer gear shaft and the outer eccentric block to rotate by corresponding degrees, the angle of the inner gear shaft and the angle of the inner eccentric block are kept unchanged under the action of the vibrating motor, the aim of changing the included angle between the outer eccentric block and the inner eccentric block is achieved, namely, eccentricity is combined, and therefore the amplitude of the vibratory roller is changed, and stepless modulation of the amplitude of the vibratory roller is achieved under the control of the hydraulic system.