In order to reduce the complexity and development cost of the multi-band all-sky imager, a multi-band all-sky imaging optical system with no focusing and high robustness is proposed. A secondary imaging system is composed of a telecentric fisheye lens and a finite conjugate distance imaging lens of the telecentric image. The shelf-level narrow-band filter is placed at the image plane, using H-FK61 and KF2 glasses achieve full system apochromatic. The design results show that the system F number is 2.8, the band range is 427.8~865 nm, the chromatic focal shift is less than 0.048 mm, and the optical transfer functions of the eight observation channels of the system are all above 0.46, which meets the application requirements. The tolerance of filter is very loose. The surface tolerance PV is less than λ/2, the refractive index tolerance is ±0.003, the thickness tolerance is ±0.05, and the shelf-level products can meet the application requirements. Compared with the traditional scheme, the system eliminates the detector focusing mechanism and does not need to use a customized narrow-band filter, which simplifies the system and reduces the cost.