Transport characteristics of cadmium in 4 soil-water systems were studied. The results showed that the diffusion coefficients of cadmium ranged from 5.6×10^-8 to 9.3×10^-7cm²/sec. Comparison between the parameters from the single and two-surface Langmuir equations demonstrated that the maximum adsorption capacity (b₂)of low-energy sites was much greater than the maximum adsorption capacity (b₁)of high-energy sites, resulting in high transportability of cadmium in the soil-water system. The variation of adsorption capacity of cadmium with pH had three distinct stages, i. e., low adsorption stage at pH6.0. The adsorption capacity of cadmium was positively correlated with pH at the stable adsorption stage. The bioavailability of adsorbed cadmium increased with increasing pH when pH<6 but decreased with increasing pH when pH<6.