Thermal radiation and vacuum lead to the deformation of bearing cylinder with carbon fiber composites which generates the defocus phenomenon for space optical camera. As heavier weight and higher complexity of the rigid focusing mechanism for the space optical camera, a novel compliant focusing mechanism with lighter weight and simple structure was designed and tested in this paper. In order to achieve stroke range and ensure image quality for the compliant focusing mechanism, micro driving displacement from the piezoelectric ceramics was amplified by two-stage flexible hinge lever-type mechanism. Taking the size parameters of the flexure hinges and beams as the design variables, an optimization model of the compliant focusing mechanism was established in which minimizing weight was considered as objection function under the stroke requirements. Consequently, optimal structure parameters of the compliant focusing mechanisms under different input forces can be obtained under the allowable stress and lighter weight. The effectiveness of the proposed compliant focusing mechanism was verified by the simulations and experiments. The results show that the compliant focusing mechanism can achieve a stroke of 2 mm for the focal plane assembly. The proposed method provided a new idea to design the focusing mechanism with lighter weight, simpler structure and higher reliability.