The metamaterial is a composite material with reasonable design. Its effective material parameters exceed the effective parameters of component materials, which shows unique properties. The concept of metamaterials has been put forward since 1960s. Nowadays, it almost involves all possible aspects of solids, from the fields of electromagnetism and optics, and mechanics and acoustics to thermology, information and other fields, and there are many research results reported, such as linear and nonlinear, reciprocal and non-reciprocal, steady and unsteady state, active and passive and so on. In this review, we start from the basics, mainly discussing the basic scope and performance characteristics of the metamaterials in optics, electromagnetism, acoustics, thermology and other emerging fields, summarizing the development process and the latest progress of theoretical design as well as experimental practices, making expectations and prospects for the future targets.