Owing to their unique mechanical properties compared to conventional materials, mechanical metamaterials have attracted a lot of attention. This unique and novel characteristic is closely related to the microstructure and geometry of mechanical metamaterials, rather than material composition. In addition, many special mechanical properties can also be obtained by designing and preparing various materials and structures. In this paper, the research progress of several mechanical metamaterials properties is reviewed, including: Strong-ultralight, negative Poisson’s ratio, negative compressibility, negative thermal expansion, and meta-fluids. In addition, the restrictive factors of the development of mechanical composite materials are summarized, and the research and development directions in this field is put forward.