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The alternating current (AC) impedance characteristics of silty soil samples have been studied by measuring their AC impedance parameters within the frequency range of 50-106 Hz. The parameters include the real part Z′, imaginary part Z″, impedance module ∣Z∣, and phase difference θ. The effects of the frequency ƒ and the water content w on these parameters are analyzed. The electrical resistivity ρs of silty soil is also calculated, and the relational expression between ρs and w is fitted. Finally, a predication formula of soil w is developed using ρs and ƒ. The results indicate that Z′, -Z″, and ∣Z∣ decrease with increasing logarithm of frequency, log ƒ, and w. Also, θ increases with increasing log ƒ, and θ does not change with w, except at ƒ = 50 and 102 Hz. Given the strong relation of Z′ with w, Z′ of silty soil is primarily determined by the polarizability of free water. In contrast, Z″ of silty soil mainly represents loss from conduction. ∣Z∣ is affected by the polarizability of free water and conduction loss. θ shows the capacitance of the silty soil. At every ƒ, an exponential function is used to simulate soil w increase with decreasing ρs, which has a very high correlation coefficient. Calculated by the predication formula, w is very close to the true w, indicating the reliability of the formula. [ABSTRACT FROM AUTHOR]