【Objective】Soil structure plays an important role in nitrogen transformation processes. Puddling, a key process of rice cultivation, generally conducted to level and prepare paddy fields for rice transplantation, greatly alters soil structure, which in turn affects soil nitrogen transformation. However, quantitative knowledge of the influence of puddling on nitrogen mineralization is still absent. 【Method】In this study, puddling practice was simulated in the lab by stirring the Hubai paddy soil in a PVC vessel and then incubated for four weeks, for investigation of effects of stirring on soil structure and organic nitrogen mineralization. The incubation experiment was designed to have three treatments in stirring intensity, i.e. no stirring (CK), a low intensity stirring (LIS) and a high intensity stirring (HIS). Soil aggregates were fractionated by particle size and their water stabilities determined with the wet-sieving method. The X-ray computed tomography and image processing technique was used to determine pore size distribution of the soil in each treatment. Mineralized nitrogen was measured with the organic nitrogen mineralization incubation method. 【Result】Compared with CK, both LIS and HIS significantly decreased the proportion of >1 mm aggregates and the mean weight diameter of water stable aggregates, but did not differ much between the two in the effect. Cumulative porosity of the soil in CK, LIS and HIS was 3.3%, 3.2% and 3.3%, respectively, showing no big difference between the treatments. However, the three treatments did show significant differences in soil pore morphology. In CK, numerous big channels high connectivity were found, while in LIS and HIS, spherical or ellipsoidal voids low connectivity were found. Organic nitrogen mineralization in LIS and HIS increased rapidly and exceeded that in CK for the first week after stirring, but declined down even below that in CK from the second week on. At the end of the incubation, CK was found to be higher than LIS and HIS in cumulative nitrogen mineralization and mineralized nitrogen potential. 【Conclusion】Results show that stirring or puddling increases nitrogen mineralization rate in the early stage, however decreases cumulative nitrogen mineralization in the end. Correlation analysis shows that soil organic nitrogen mineralization is significantly and positively related to macroaggregate content and 30~100 μm pores. However, more studies are needed to differentiate the effects of aggregate breaking down and pore restructuring on nitrogen mineralization as a result of puddling.