An expandable modular energy-dissipation protection net unit group includes support columns each provided at each of two ends of each support column with a first horizontal longitudinal rotation reversing device on the left side, a second horizontal longitudinal rotation reversing device on the right side and a transverse rotation reversing device on the bottom; a transverse endless support rope, a longitudinal endless support rope and connectors. The transverse endless support rope is wound on the transverse rotation reversing device. The longitudinal endless support rope is wound on the first horizontal longitudinal rotation reversing device and the second horizontal longitudinal rotation reversing device adjacent. A metal net panel is tied by the plurality of connecting members and hung on the transverse endless support rope and the longitudinal endless support rope.