Limb sounding technique is an important tool for remote observations of Earth’s middle atmosphere.It aimed at an altitude of about 10—100 km.Compared with the nadir viewing

limb sounding has a higher vertical resolution.Recently

sub-millimeter（0.1—1.0 mm or 300 GHz—3 THz） limb sounding technique has been developed

which can detect the halogen elements a ssociated with the O 3 processes

a special significance for atmospheric environmental monitoring of the ozone layer.This study o verviews five limb sounders（Odin/SMR

EOS AURA/MLS

JEM/SMILES

MASTER and SOPRANO） and their reversion s ystems.Sub-millimeter limb sounding from space has several advantages.The sounders always have higher spectral resolutions and broader bandwidth.Furthermore

many trace gases have spectral emissions in sub-millimeter ranges.Sub-millimeter limb sounding can provide many species of Cl y and Br y with higher precision.The uncertainty of the retrieval profiles of ClO and HCl can be less than 10%.All the reversion systems of the five sub-millimeter limb sounders are based on the OEM（Optimal Estimation Method） with Gauss-Newton or Levenberg-Marquardt iterative.Since the sub-millimeter limb sounding can reach troposphere

the forward model has to consider the multi-scattering by clouds.