Since 1977 microwave brightness temperature of wet soil have been measured by multi-frequency （1.4

5.4

9.2 and 36 GHz） radiometer designed by Changchun Institute of Geography

Academia Sinica. The relationship between dualpolarized brightness temperature and soil moisture has been experimentally obtained. In numerical simulation

wet soil was modeled as stratified

half-space dissipated media. By using the dyadic Green’s function of stratified media and the fluctuation-dissipation theorem

thermal radiance from such media may be calculated. However

in the previous approaches of the fluctuation dissipation and radiative transfer

the functional dependence of practical soil dielectric profile with soil temperature

wetness

soil structure and so on were lacking. By employing the empirical formulation of multi-phase mixture for soil dielectric profile

and applying the fluctuation dissipation approach in WKB method

we developed a numerical model to simulate the brightness temperature versus soil surface wetness

frequency

observation angle

etc.. Our numerical results are shown to agree well with multi-frequency data measured in our Jing Yu Tang Remote Sensing Site. We also discuses in this paper the contribution from weighting function in radiative transfer at different depth for multi-frequency

and the effects due to wetness and temperature profiles

polarization

and observation angle. It does show quantitatively the functional dependence of brightness temperature on these conditions. Sensitivity of some parameters

such as wetness transition which is closely related with soil structure

is also tested.