The invention discloses a periodic cavity type vibration isolator with low frequency and a broad-band gap and a preparation method. The vibration isolator comprises two or more than two periodic units. Each periodic unit comprises two thin plate main bodies and a ring cavity scattering body, wherein outer edges of the two thin plate main bodies are connected by virtue of the ring cavity scattering body to form a cavity; and the periodic units are connected through a connecting block scattering body. The preparation method comprises the following steps: selecting materials to prepare the thin plate main bodies, the ring cavity scattering body and the connecting block scattering body; regulating geometrical parameters of the thin plate main bodies, the ring cavity scattering body and the connecting block scattering body, so that effective band gap frequency of the vibration isolator can cover vibrating frequency of a required vibration isolating environment; checking whether the vibration isolator meets a safety condition or not so as to prepare the periodic cavity type vibration isolator with low frequency and the broad-band gap. The periodic cavity type vibration isolator disclosed by the invention is suitable for isolating low-frequency vibration, can realize vibration isolation within a wide frequency range while keeping corresponding bearing capacity, can form a band gap at a lower-frequency band, and has a boarder band gap, a relatively small dimension, and higher vibration attenuation rate.