The present invention relates to an elastic metamaterial for reducing vibrations of a flexible structure such as a main cable of a tether system for controlling an orbit of a satellite revolving around a planet, and a method for improving a vibration reduction performance thereof, and more particularly, to an elastic metamaterial having an improved precision, in which a ratio of a cross-sectional area of a pendulum ring may be adjusted to maintain a frequency characteristic other than a band gap generated due to the elastic metamaterial even in a state where a mass of the pendulum ring is not changed, and a band gap (R_ring) generated due to the pendulum ring of the elastic metamaterial and a band gap (R_beam) generated due to the elastic beams may be combined into one band gap to expand a vibration damping range, and a method for improving a vibration reduction performance thereof.