Taking the paddy field soil of Wuhan City in Hubei Province as the study object, an experiment of dry and wet alternate culture was carried out in which three treatments were designed: without adding Chinese milk vetch(CK), adding 2% Chinese milk vetch(G1), and adding 4% Chinese milk vetch(G2), the composition of soil aggregates and the distribution characteristics of organic carbon in soil aggregates at 60 d, 120 d and 180 d of culture were measured and compared. The results showed that the content of > 2 mm aggregates was increased by adding Chinese milk vetch for 120 days, at 60 d the maximum increase was observed for G1 treatment (78.08%) and at 120 d the maximum increase was observed for G2 treatment (77.31%), and adding Chinese milk vetch also significantly increased the mean weight diameter of soil aggregates. Organic carbon contents increased with adding Chinese milk vetch in different culture periods, and organic carbon content of G2 was higher than that of G1. Organic carbon contents in all treatments first increased and then decreased with the increase of culture time. The content of organic carbon in soil aggregates decreased with the decrease of aggregate size. Adding Chinese milk vetch for 180 d increased the contents of organic carbon in all sizes of soil aggregates, and the organic carbon content of > 2 mm aggregates increased the most (17.17% ~ 43.67%). Adding Chinese milk vetch for 120 d mainly increased the relative content of organic carbon fractions in macroaggregates, while for 180 d significantly increased the content of fine particulate organic carbon in microaggregates.