Purple soil and yellow soil from Three Gorges Reservoir area are submerged and incubated under a nitrogen atmosphere at constant temperature (25℃) to study the dissimilatory iron reduction processes and its effect on chemical form of Fe. The results show that pH and ORP decrease with the transition of soil redox condition, and it is especially obvious for yellow soil. The content of Fe(Ⅱ) increases to 3 495.21 mg/kg for yellow soil and 536.44 mg/kg for purple soil. There are no obvious changes of redox condition and Fe(Ⅱ) for sterile soil. It suggests that dissimilatory iron reduction should be driven by metabolic activity of microbe. With the transition of soil redox condition, the content of oxide-Fe increases significantly, and the content of Fe(Ⅱ) and oxide-Fe are significantly and positively correlated, which indicate that transformation of Fe speciation is the result of dissimilatory iron reduction.