Samples of paddy soil were prepared into slurry and then incubated anaerobically at a constant temperature for exploration of effects of illumination on reduction of sulfate and redox of iron in the soil. Water soluble inorganic carbon and organic carbon in the soil were analyzed simultaneously for relationship of anaerobic redox process of iron with sulfur and carbon transformation under illumination in the paddy soil. Results showed that illumination is a key environmental factor regulating geomicrobiological cycling of iron and sulfur. Inhibitive effect of illumination on reduction of iron and sulfur was observed after 5 days of anaerobic incubation. After 30 days of anaerobic incubation in the dark, 70.07% of free iron was reduced in the soil; and in the soil incubated under illumination, 35.60 μmol g⁻¹ Fe(III) was reduced first and then re-oxidized, and after 30-days, the soil still had 32.70% of its free iron reduced. After the illumination was turned off those oxidized Fe could once again be reduced and 99.50% of the water soluble sulfate in the soil was reduced within 5 days. In soils anaerobically incubated for 30 days under illumination, 42.73% of the WSS was reduced. The date when the maximum reaction rate of iron reduction or oxidation appeared came prior to the date when maximum reaction rate of sulfur transformation was observed. Close relationship of water soluble inorganic carbon with Fe(II) and water soluble sulfate in the soil were found, and significant positive relationships were also found of water soluble organic carbon (WSOC) with iron or sulfur transformation rate in the soil under incubation without shifting between illumination and darkness. In the soil under dark incubation when WSOC in the soil was > 7.89 μmol g⁻¹, Fe(III) and water soluble sulfate (WSS) tended to be reduced, while in the soil under illuminated incubation, when WSOC was > 8.27 μmol g⁻¹, Fe(III) did and when WSOC was > 8.40 μmol g⁻¹, WSS did.