Samples of paddy soil were prepared into slurry with water in different ratio and then incubated anaerobically in dark and under light at a constant temperature for exploration of effects of water content on iron redox and, water soluble carbon content in the soil and, CO₂ and CH₄ emissions from the soil. Results show that water content and illumination are key environmental factors regulating iron redox process and transformation of its coupled carbon. Higher water content accelerated appearance of the peak iron reduction rate in and promoted CH₄ emission from the soil under incubation in dark. In the soil lower than 50% in water content incubated under light, increase in water content stimulated re-oxidation of ferrous iron, while in the soil higher than 50%, a reverse effect was observed. In the soil incubated in dark increased water content increased the content of water soluble inorganic carbon (WSIC), which was significantly and positively related to CH₄ emission. However, in the soil incubated under light, increased water content reduced the content of WSIC with an extent expanding with increasing water content. In the soil with water content ranging from 25% to 200%, light reduced CO₂ and CH₄ emissions by 95.80% and of 96.08%, respectively.