The present invention discloses a stiffness-adjustable electromagnetic spring. The electromagnetic spring includes a central shaft, an intermediate electromagnetic force control component, and two end electromagnetic force control components, where the two end electromagnetic force control components and the intermediate electromagnetic force control component are both sleeved on the central shaft, and an intermediate controllable power supply in the intermediate electromagnetic force control component is used to control an electromagnetic force of an intermediate coil on a ring magnet and a two-end controllable power supply in the two end electromagnetic force control components are used to control an electromagnetic force on the ring magnet, therefore, the stiffness of the electromagnetic spring can be controlled online and the nonlinearity can be adjusted. The stiffness-adjustable electromagnetic spring disclosed in the present invention can generate adjustable negative stiffness to decrease the dynamic stiffness without reducing the static stiffness, thus break through the limitation of carrying capability of the spring on the vibration isolation performance, and has characteristics of compact structure, fast response, easy control.