Vibration damper for ship shaft system and vibration damping method of vibration damper

The invention discloses a vibration damper for a ship shaft system. The vibration damper comprises a shaft and a cabin wall for supporting the shaft, two shaft sleeves, two bearings, one barrel-shaped base body and a vibration damping cover which are subject to axial isolation are sequentially and fixedly installed between the shaft and the cabin wall in a sleeving manner from the outer circle of the shaft outwards, the vibration damping cover and the base body are in sealed connection to form a sealed annular cavity body, the cross section of the annular cavity body is in an arc taper shape, and a flange is arranged at the top of the arc taper; a ring-shaped vibration damping sheet provided with a plurality of through holes and extending into the annular cavity body is fixedly embedded at one end of the flange, and the other end of the flange is fixedly connected with the cabin wall; and an oil adding valve and a gas discharging valve which are communicated with the annular cavity body are arranged on a cove