This study investigates a miniaturized multifunctional optical system based on a multiband image fusion system. The miniaturized multifunctional optical system solves the problems of large volume, heavy weight, and delayed white-light observation in the original system. The miniaturized multifunctional optical system comprises four modules. The energy convergence of the laser module is greater than ϕ1 mm. The modulation transfer function of the low-light-level module is 53 lp/mm, which is favorable. The magnification of the white-light module is 5.7^×. Additionally, the central and edge fields-of-view are greater than 5.7′ and 17.1′, respectively. The modulation transfer function of the image-observation module in the center field-of-view at 62 lp/mm is greater than 0.3. The miniaturized multifunctional optical system reduces the volume of a multiband image fusion system from the original 261 cm×237 cm×115 cm to 220 cm×173 cm×102 cm, and the weight is reduced by 496.6 g. Therefore, this miniaturized multifunctional optical system offers a certain reference value.