The differential absorption spectrometer has the following technical indicators: the field of view 114°×0.5°, high spectral resolution 0.3～0.5 nm, and high spatial resolution 13 km×48 km. In order to achieve the indictors, the optical system and three-dimension mechanism are designed including elevating mechanism, swaying mechanism, and rotating mechanism. The elevating mechanism can be adjusted between ±150 mm with the resolution 0.05 mm in the vertical direction, and meets the requirement for the position adjustment of the spectrometer. The swaying mechanism can sway between ±3° with the resolution 3′. The rotating mechanism can rotate between ±62° with the resolution 5″.