Owing to its unique terahertz properties, graphene has potential applications in terahertz sources, terahertz detection, and terahertz control. In this paper, the terahertz properties of graphene and graphene-based terahertz devices are reviewed; further, the potential applications of graphene in the aforementioned fields are prospected. As for the terahertz properties of graphene, this paper mainly introduces the conductivity model, the characteristics of equilibrium and ultrafast spectral response, and the properties of surface terahertz wave emission. As for the graphene-based terahertz devices, this paper mainly reviews the recent developments in the research on the active terahertz devices based on optical, electrical, and magnetic control, the terahertz modulators with graphene-based metamaterial, the antireflection devices based on impedance matching, and the tunable terahertz sources.