Abstract: To meet the requirements of integrating day and night in electro-optical sights, lightweight design, and excellent stability, a dual-band co-aperture digital aiming objective lens that was visible and near-infrared was designed, and used a CMOS camera to receive the imaging beam. The optical system was designed for the wavelength ranges of 0.4 µm~0.65 µm and 0.7 µm~0.85 µm, with a focal length of 50 mm, an F-number of 1.4, and a total length of 90 mm. The system shows no thermal difference effects in the temperature range of −40 °C to 50 °C, with distortion in each band less than 0.04%. In the visible light band, the modulation transfer function (MTF) is greater than 0.55 at 100 lp/mm, and in the near-infrared band, the MTF is greater than 0.3 at 100 lp/mm. By optimizing the aberrations caused by the sensitive surface of the system and properly distributing the optical power, the sensitivity of the system to processing tolerances, assembly difficulty, and cost were reduced. The design results show that the system uses spherical mirrors, making it simple in structure, small in size, low in cost, and with good tolerances, which can achieve good imaging quality across the entire operating temperature range, and has a certain engineering application prospect.