Mechanical metamaterials are a category of artificial structural materials and essentially composite structures constructed with artificial microstructure units, which aim to enhance mechanical properties of macroscopic overall structure by designing the shape, size and periodic arrangement mode of artificial microstructure units, and to achieve extraordinary mechanical properties such as negative Poisson’s ratio, multi-stability, lightweight and high strength, and programmability/reprogrammability. However, mechanical metamaterials fabricated by conventional materials are difficult to meet the performance requirements of multi-environmental field adaptability, rapid and controllable environmental response, and energy conversion for functional devices in different engineering application scenarios. Mechanically functional metamaterials constructed by combining mechanical metamaterials with advanced functional materials expand the performance of mechanical metamaterials from the material perspective, and can achieve tunable electro-mechanical, magneto-mechanical and thermo-mechanical coupling responses, which are expected to realize the multifunctional engineering applications of mechanical metamaterials. This review describes the extraordinary mechanical properties and typical classifications of mechanical metamaterials, detailly introduce the construction methods and coupling responses of three representative mechanically functional metamaterials, namely electro-mechanical, magnetomechanical and thermo-mechanical metamaterials, and summarizes and prospects the potential engineering applications of mechanically functional metamaterials in the fields of aerospace and marine engineering, including self-folding satellite solar wings, micro-spacecraft self-powered, satellite platform vibration isolation, marine engineering and equipment monitoring and sensing, and marine wave energy harvesting.