Structure and composition of one hybrid mono-directional magnetic force spring was presented. based on the experiment rig of magnetic force spring the magnetic force characteristics and its influencing factors were experimentally studied and analyzed. research results show that the stiffness of the hybrid magnetic force spring composed of the electromagnet and the permanent magnet is adjustable and controllable. as a whole the axial magnetic force of the hybrid mono-directional magnetic force spring increases non-linearly with the air gap between magnets decreasing within small air gap, namely the magnetic force spring behaves negative stiffness characteristics. the axial magnetic force is decided by the magnet with less magnetic field energy. and the adjusting range of the axial magnetic force depends on the two magnets' dimensions, their surface magnetic flux density and the magnetic saturation degree of the eletromagnet. furthermore, under same air gap the axial magnetic force of the magnetic force spring increases linearly with the excitation coil voltage increasing.