Purple soil and yellow soil of Three Gorges Reservoir Area were submerged and incubated under a nitrogen atmosphere to study the effect of redox process on chemical form of Cd. It is shown that the pH and Eh decrease in the redox process. With the transition of soil redox condition

the content of CEC increases to 1753 cmol·kg -1 for purple soil and 2794 cmol·kg -1 for yellow soil

and the content of Fe (II) increases to 3 15630 mg·kg -1 for yellow soil and 44656mg·kg -1 for purple soil. The soluble Cd concentration declines after submergence for the purple soil and yellow soil

and 99.9% of soluble Cd is absorbed by soils. Chemical form of Cd in soil is significant correlated with the physical-chemical indexes of soil. In the process of redox process

part of Exc-Cd (exchanged fraction) transforms to Carb-Cd (carbonated fraction) and Oxide-Cd (oxide-bound fraction)

and the content of Exc-Cd decreases to 456 mg·kg -1 for purple soil and 102 mg·kg -1 for yellow soil. The stability of Cd in yellow soil is higher than that in purple soil.