Particulate Observing Scanning Polarimeter (POSP) is a spaceborne spectropolarimetric sensor to map radiometric and polarimetric information of global atmospheric particulate matter. POSP has three SWIR bands, respectively are 1.38μm, 1.61μm and 2.25μm. So the SWIR polarimetric system is designed, which has the characteristic of division of aperture and division of amplitude to realize the simultaneous polarization measurement. The system has two identical optical paths, their orientation is 45 degree, and it can measure first three Stokes parameters. In order to realize to cool the InGaAs detectors below -60°C, combined with active cooler and passive cooler, the InGaAs detectors assembly and cooling system are integrated compact. The thermal vacuum test shows that cooling system could meet the cooling requirements of InGaAs detectors.