Abstract: Mechanical metamaterials exhibit many counterintuitive mechanical properties by changing their internal geometry. We propose a mechanical metamaterial composed of gears as basic elements. The gear-based mechanical metamaterial proposed here is a multi-stable structure， which can be continuously converted between various stable states through the meshing of gear teeth. The continuous switching between states enables the mechanical metamaterial to exhibit in situ continuously tunable mechanical properties. The mechanical properties of the mechanical metamaterials were studied by using the finite element method. The results show that the gear-based mechanical metamaterials exhibited continuously adjustable stiffness， variable generalized shear stiffness， and adjustable acceleration transmissibility. These unique properties of mechanical metamaterials provide new ideas for creating programmable metamaterials with in situ continuously adjustable mechanical properties， and are expected to be applied in the fields of smart materials and engineering.