To solve the problems of large volume and chromatic aberration in the distributed-aperture optical system working in multi-waveband environment, a refractive optical system is proposed as an alternative, in which the visible light and Long Wave Infrared(LWIR) share the mutual aperture and prism splitter.The mutual optical path of different wavebands is realized by utilizing certain kinds of materials that both visible light and LWIR can pass through.The optical system adopts the passive athermalization design.The design result suggests that, for the visible light working in the range of 0.55~0.75 μm and LWIR working in the range of 7.5~9.5 μm, their focal length is 120 mm and the F number is 2.8.The MTF for visible light is above 0.5 at a spatial frequency of 90 lp/mm, while the MTF for LWIR is above 0.4 at a spatial frequency of 17 lp/mm.Athermalization is realized in the temperature range of -40~+60℃.