The purpose of this paper is the capacity of spectral reflectance, in the full optical domain 0.4 - 12 μm, to retrieve the Soil Moisture Content (SMC) of bare soils. For this, a new empirical soil model was performed from spectra lab measurements, and more precisely from soil's classification, to simulate spectral reflectance for a given SMC, and in inverse way to estimate SMC. In solar and thermal domain, simulated spectra are highly correlated with measured spectra, respectively with 98% and 85%. In inverse way, estimation of SMC from a spectral reflectance and a given soil classes, provides a RMSE of 3.2% in solar and 2.8% in thermal domain.