A damping device includes a cylinder in which a resilient member and a piston are received. A cover assembly and a seal member seal the cylinder and damping medium is filled in the cylinder. The piston includes a piston body, a connecting portion connected with one end of the resilient member, and a neck portion connected between the piston body and the connecting portion. The piston body has an opening penetrating through the piston body. A control valve is movably mounted to the neck portion to control the opening during operation. A piston rod has one end connected with the piston body and another end extending out from the cylinder. A damping member is located between the piston and the cover assembly. The traveling velocity of the piston is controlled by the control valve to close or to open the opening through which the damping medium passes.