Taking the oxygen absorption band A as an example, we consider some constraints of the system such as detection distance, target and background signal-to-noise ratio(SNR), system operating altitude on the channel bandwidth based on the selection rules of number and position of ranging spectrum channels, and simulate and analyze the range of the channel bandwidth upper and lower limits to meet the real-time performance of system, target SNR and different detection distance conditions by using MODTRAN and MATLAB softwares. The results show that the higher the platform altitude is, the lower the lower limit of bandwidth is, the larger the range is, the more flexible the selection is, the longer the system detection distance is and the larger the effective detection range is under the same conditions; the higher target SNR requirement is, the larger the lower limit of bandwidth is, the smaller the detection range is, the less flexible the selection is, the smaller the effective detection range and scope are under the same conditions. Therefore, in the design of passive ranging system, we should firstly determine the location and number of spectrum channels based on the task design requirements, and then calculate the upper and lower limits curves of each channel under multiple constraints of the real-time system, the signal to noise ratio, and the maximum and minimum working distance of the system. Secondly it will be determined that the minimum intersection based on the upper and lower limit curves that satisfy both the minimum and maximum working distance. Finally, the best channel bandwidth values that meet the design requirements could be selected in the intersection. It can provide an effective theory support and calculation method for the parameter design and engineering of single-lens multi-spectrum passive ranging system with arbitrary precision and arbitrary distance.