In order to ensure that the space infrared camera obtained a light and reliable sweeping head, and the mirrors had good surface accuracy and a high first-order natural frequency for the space sweeping camera system, the structure of sweeping part was studied in a targeted manner. The beryllium-aluminum alloy material was selected as the Φ750 mm diameter main mirror material, the flexible support structure of the titanium alloy material was selected as the support structure, and installed in the main mirror chamber of the beryllium-aluminum alloy material. It included a secondary mirror assembly, a secondary mirror support part and a light-shielding cylinder. The total weight of the entire swinging part was 17.5 kg. The finite element method was used to simulate the mirror assembly under the condition of force and heat coupling. The results show that the maximum surface error RMS of the mirror is 27.04 nm, which is no less than λ/20 (λ=632.8 nm) in the full aperture range requirements. The first-order resonant frequency of the oscillating portion is 122 Hz, which reserves a large bandwidth for the control system. The mechanical test results of the solid model are close to those of the finite element analysis, indicating that the overall design requirements for the sweeping part are met.