For on-axis three mirror astigmatism (TMA) space camera with large aperture and long focus, the secondary mirror support is a big mass cantilever. In order to improve the dynamic characteristics and ensure support structure stability, a lightweight support structure with high stiffness and stability is designed by theory and finite element analysis. The assemble weighs less than 4.5 kg. The analysis and test results show that the frequency of the first mode is 104 Hz and the dynamic characteristic is good. The dimension stability is less than 3 μm through dynamic vibration and thermal vacuum circle by self-designed method and device, and the structure size does not change. Stability test results show that the barrel design is reasonable and has high stability. At present, the support structure is adopted in some high resolution space camera, which would be referenced by high resolution, lightweight, and agile camera design.