The structural complexity of soil dissolved organic matter (DOM) may reflect soil biogeochemical processes due to its spectral characteristics.  However, the features of DOM structural complexity in paddy soil amended with long-term chemical P fertilization are still unclear, which may limit understanding of nutrient-related soil C cycle.  We collected soil samples from field experiments receiving application of 0, 30, 60, and 90 kg P ha^–1 yr^–1 to assess the effect of exogenous P on the complexity of soil DOM structure.  Three-dimensional excitation-emission matrix fluorescence analysis and enzymatic activity assay were used to determine the features of soil DOM molecular structure and the associated microbial reactions.  The results showed that P input increased the biodegradability of DOM, indicating by the increased lower molecular weight components and decreased humic degree in the DOM.  P input also reduced the structural complexity of DOM with blue shifts of fluorescent signals.  The fluorescence index and β/α index of DOM increased with increasing P application by 4–5% and 3–11%, respectively, while humification index decreased by 8–13%.  The P input increased the abundance of bacteria and fungi by 34–167% and 159–964%, respectively, while 29–54% increments were found for the β-1,4-glucosidase activities.  These results implicated that P fertilization accelerated the soil DOM cycle, although the structural complexity of DOM declined, which potentially benefits soil C sequestration in paddy fields and may be a C sequestration mechanism in the P-dependent paddy.