The invention discloses an ultralow frequency vibration isolator based on parallel connection of a positive stiffness spring and a negative stiffness spring, comprising a guide post, a sheath cover, a sliding block, a negative stiffness spring, a lower cover, a guide seat, a ball and a main spring. According to the invention, the main spring (a positive stiffness spring) is connected with the negative stiffness spring in parallel, thus a vibration damper can have the characteristics of high static stiffness and low dynamic stiffness, and zero-hertz ultralow frequency vibration isolation is realized; connection of a screw thread pair is adjusted, thus a stiffness curve of a vibration isolator is adjusted according to vibration isolation quality, and vibration isolation performance can be adjustable; and rolling friction is realized by adopting balls, thus frictional resistance is reduced. The ultralow frequency vibration isolator disclosed by the invention can be used as one component and is applicable to an environment under vibrational excitation, especially an environment under low frequency vibrational excitation, such as a vehicle seat, a suspension, precise instrument vibration isolation as well as vibration attenuation and seismic resistance.