In the past two decades,GNSS-R has been emerged as a new and attractive remote sensing technique.The geodetic/geophysical GPS receivers are out-of commercial and their recorded SNR data have potentials for geophysical parameters detections,e.g.soil moisture,vegetation growth and snow depth.Based on the developed forward GP multipath model,effects of bare soil parameters on GPS multipath observations are evaluated here.Wave synthesis technique is employed to get the coherent scattering coefficients at VV,HH,RR and LR polarizations,while the bare soil dielectric constant is calculated by a microwave dielectric soil-water mixing model.Effects of three-frequencies GPS modulations (L1 band,L2 band and L5 band) are evaluated: although there are apparentdifferences for GPS multipath observables,it is not the effects of bare soil but the direct broadcasting signals since the soil scattering properties at these frequencies(L band)are the same.Soil texture and surface roughness has almost no effects on GPS observables.As the soil temperature changed from below zero to above zero,the amplitudes of SNR,phase and code pseudorange increased.Soil moisture also affects the GPS observables,as moisture content increases,the amplitudes of GPS observables increase.