The invention provides a hydraulic dewatering machine, and a sludge dewatering system and method, and belongs to the field of environmental protection equipment. The hydraulic dewatering machine comprises a rack, a hydraulic system, a dewatering device and a starting-up device; the hydraulic system provides the pressure for the dewatering device; the dewatering device is used for extruding sludgeto dewater; the starting-up device is used for driving to start up the dewatering device to make sludge fall. The sludge dewatering system includes the hydraulic dewatering machine and a plate overturning dewatering machine. The plate overturning dewatering machine is used for preliminary dewatering, and the hydraulic dewatering machine is used for deep dewatering. The dewatering system is adoptedin the method. With adopting of the hydraulic dewatering machine, and the dewatering system and method, the dewatering rate is high, the labor intensity of workers is reduced and the dewatering efficiency is improved.