In large-aperture and long-focus space remote sensing cameras， the relative position changes between the primary and secondary mirrors affect the imaging quality and stability of the camera. The support structure between the primary and secondary mirrors， that is the bearing structure between them， is integral for the camera design process. In this study， a carbon fiber thin-walled cylindrical support structure between the primary and secondary mirrors was designed， based on the characteristics of large-aperture and long-focus cameras. First， the cylindrical base structure was selected depending on the optical system considered. Then， based on the characteristics of the cylindrical base structure， the geometric structure of the secondary mirror support beam and the longitudinal reinforcement ribs of the cylindrical structure were analyzed and selected in sequence. Subsequently， to fully utilize the design characteristics of the carbon fiber material layup， the iterative design optimization of the key size of the support structure， thickness of the layup， and angle of the layup was performed， and the design results were analyzed by conducting finite element simulations. Finally， the stability and structural rigidity of the support structure were verified by measuring the change in the angle of the secondary mirror and conducting the characteristic-level sweep frequency vibration test. The results indicated that the differences in long-term monitoring under the same conditions for the secondary mirror was less than 1.5"， change before and after gravity flipping was less than 1.08"， first-order natural frequency of the supporting structure was greater than 115 Hz， and axial frequency was greater than 180 Hz. Thus， the support structure between the primary and secondary mirrors exhibited excellent rigidity and structural stability， satisfying the requirements of the design index.