In order to study chemical speciation and bioavailability of cadmium in the soil-plant systems, 1, 3,8, 15, 30 mg·kg^-1 exogenous cadmium were dropped into the brown soil, and morphology of cadmium and qualityscores in soil were detected under different concentrations and different treatment time. The results showed that withthe increase of concentration of exogenous cadmium, carbonate and organic soil cadmium would convert into ex-change state and residual cadmium, but almost Fe-Mn oxides would not change. With the last of time, soil exchange-able and carbonate bound would change to residual cadmium, Fe-Mn oxides and organic-bound cadmium, thus bio-availability of cadmium decreased.