Decomposition and distribution of carbon derived from organic materials in paddy soils in the red soil region of subtropical China as affected by moisture regime (aerobic, flooding and wet-dry alternating) were investigated in laboratory through incubation experiments. Results indicate that organic material decomposition rate was the highest in the soil under wet –dry alternation and the lowest in the soil under flooding. Amendment of organic materials promoted mineralization of soil original carbon native in the soils under aerobic and flooding conditions, displaying a positive priming effect, but reversely in the soil under wet-dry alternation, showing a negative priming effect. The priming effects weakened with the incubation going on. ΔlogK and E4/E6 ratio of humic acid was significantly lower in the soil amended with organic material under wet-dry alternation than in the soils under flooding and aerobic conditions. Flooding made humic acid in the soil simple in structure, while wet-dry alternation made it complicated, with enhanced aromatization and humification. The distribution ratio of organic material-derived carbon in soil humus fractions showed that wet-dry alternation and aerobic condition promoted formation of humic acid, conversion of fulvic acid fraction and decomposition of humic acid fraction native in the soils. In the soil under flooding, the carbon derived from organic materials accounted for a high proportion in soil fulvic acid fraction and inhibited decomposition of soil native humic acid components. A high proportion of the carbon derived from organic materials was distributed in > 0.053 mm aggregates, which was especially obvious in the soil under wet-dry alternation and flooding.