Conventional triboelectric generators (TEGs) have been developed to mainly harvest the energy of linear mechanical motions and convert it usually into oscillating or pulsive, but not sustainable, electrical outputs. In this study, unidirectional charge transfer mechanisms are introduced to develop a triboelectric mechanical metamaterial (TMM) with sustainable electrical outputs. Density functional theory and experimental analyses demonstrate three minimum necessary components of TMMs fabricated by only two triboelectric materials (i.e., copper and PTFE) to generate sustainable electrical outputs. Under a wide range of compression-tension strain of ±50%, the maximum open-circuit voltage, short-circuit current, and volumetric power density are 3860 V, 8 µA, and 365.3 kW m−3, respectively. Different from most conventional cellular solids, the mechanical energy dissipation of the TMMs increases quadratically with the unit cell number. High volumetric electromechanical efficiency is achieved when the unit cell is miniaturized. In addition to energy harvesting and mechanical energy dissipation, TMMs can sense the displacement by counting the number of distinctive peaks in the short-circuit charge transfer or reaction force versus time curves. The extreme electromechanical functionalities of the TMMs facilitate their applications in intelligent suspension systems, miniaturized green power sources, and self-sensing energy harvesters.