Based on a 2 m lightweight SiC primary mirror, a new type of active adjusting lateral support mechanism was designed. Firstly, the structure forms and characteristics of the commonly used lateral support mechanism were analyzed; and then the active adjusting support mechanism composed of displacement actuator, flexible hinge structure and embedded lever system was designed. Finally, the finite element analysis of the support force and the displacement of the mechanism were carried out, and the experimental platform was built to test the stiffness and the energy-saving ability of the mechanism. The experimental results show that when the supporting force is 562.55 N, the force acting on the displacement actuator in the lever structure is 97.57 N, and the stiffness and strength requirements of the displacement actuator are greatly reduced; The stroke of the displacement actuator is 0.065 mm, which is 22 times that of the supporting rod, and greatly reduces the resolution requirement of the displacement actuator; The stiffness measured by the experiment is 1 225 N/mm, which meets the design requirements. It shows that the flexible lever support system has good engineering application ability.