Based on the fundamental theory of improving structure stability, an initial structure of target chamber system was designed. With finite-element method (FEM), modal analysis was proceeded for the target chamber system, thus the weak links were found. Based on the weak links of initial structure, the initial structure of target chamber system was optimized. At last, the stability analysis was proceeded for the target chamber system. The results of analysis indicates that the target chamber system can obtain good stability, when the thickness of target chamber (T) is 50 mm, the angle of support leg to vertical direction (θ) is 27.2°, the rib with thickness B of 20 mm is added between the support legs, and the space distance of the rib is 120 mm. The translational displacement root-mean square (RMS) is 1.425 μm which satisfies the stability requirement of target chamber system in SGⅡ upgrade facility.