In the past decades, terahertz metamaterials have attracted considerable attention due to the capability of realizing essential terahertz functional devices and potential applications in sensing, imaging, spectroscopy and monitoring. In this review, we first present a brief introduction to the theory and development of terahertz metamaterials, and then focus on some terahertz devices including both triple-band and broadband metamaterial absorbers, the spoof surface plasmon polaritons (SPP) waveguides, the SPP bend, the SPP beam splitter, and the SPP ring resonator. The metamaterial absorbers are fabricated and measured in THz band, while the SPP devices are verified through numerical simulations. All the designs are easy to fabricate and favorable for practical applications.