A micro-electro-mechanical system based focusing device and manufacturing method thereof are disclosed. The system includes: a deformable lens, multiple groups of conductive deformable crossbeams and conductive structs; and one or more fixed parts. In each group, each conductive deformable crossbeam corresponds to a conductive struct. The conductive deformable crossbeams and the conductive structs are arranged around the deformable lens and spaced from each other. The conductive deformable crossbeams are suspended in the air, their inner edges are connected with an external edge of the deformable lens and their external edges are connected with the fixed parts. The conductive structs are fixedly connected with the fixed parts and remain stationary. Electrostatic force between the conductive deformable crossbeam and the conductive struct causes the deformable lens to be stretched and rotate, thus, surface curvature and focal length are changed. The device has a small size, low power consumption and low manufacturing cost.