The present invention relates to a rebound composite electromagnetic energy dissipation device for reducing sloshing with a liquid-filled ball for a large liquefied natural gas (LNG) storage tank. When the liquid surface sloshes around, the gas spring is pulled by the steel strand to produce vertical displacement and provide a restoring force, and the vertical displacement of the gas spring drives the fan blades on the sleeves of the ball screws at the bottom to rotate in the damping fluid, consuming energy. The present invention uses hydraulic transmission instead of mechanical transmission of traditional piston motion, and the horizontal pistons produce horizontal displacement in the case of pressure unbalance, thus increasing the flexibility of horizontal piston motion; magnets are arranged in the horizontal slideways and the horizontal pistons to intensify the motion of the horizontal pistons and the relative motion between the horizontal pistons and the interior.