the negative stiffness unit comprises an inner-ring magnet group, an outer-ring magnet group and a supporting shaft, the supporting shaft axially slides on the base and passes through the housing, the inner-ring magnet group comprises a plurality of inner-ring magnets, the plurality of inner-ring magnets all fixedly sleeve the supporting shaft, opposite ends of every two adjacent inner-ring magnets are opposite in polarities, the outer-ring magnet group comprises a plurality of outer-ring magnets, the plurality of outer-ring magnets all sleeve a periphery of the inner-ring magnet group and are divided into an upper group of outer-ring magnets and a lower group of outer-ring magnets to be installed inside the housing, and opposite ends of every two adjacent outer-ring magnets are opposite in polarities;

the upper group of outer-ring magnets and the lower group of outer-ring magnets can synchronously move towards each other or back to back along a direction of the supporting shaft through the negative stiffness adjusting device; and

axial relative positions of a middle plane of the outer-ring magnet group and a middle plane of the inner-ring magnet group can be adjusted by adjusting the axial relative positions of the housing and the base.