In this paper, the relationship between the microwave backscattering coefficient and soil moisture of bare and vegetation (sweet potato, soybean and peanut)-covered fields is discussed, and the comparision between the results of X- and C-bands is made. The study results indicate that for microwave remote sensing of the soil moisture of bare fields, when incidence angle θ=6°, the sensitivity S_v is the maximum; when θ=45°, S_v=0; and while θ>45°, the backscattering coefficient is getting lower with the increase of soil moisture.At small incidence, X- and C-bands are quite similar in the accuracy. For microwave remote sensing vegetation-covered fields, the sensitivity and accuracy of X-band are lower than those of C-band, but X-band still has a certain sensitivity and accuracy as long as proper working parameters are selected. The prediction error of soil moisture which has been estimated by a simple model proposed in this paper is about ±25% at X-band.