Exploring the change characteristics of soil aggregate, organic carbon, and bacterial communities in Robinia pseudoacacia plantation could provide a theoretical basis for soil quality and function improvement. Robinia pseudoacacia plantations with different ages (eight, eighteen, and thirty years old) and abandoned farmland (CK) in gully region of the Loess Plateau were selected as the study sites. Soil aggregates with different particle sizes were obtained through the optimal moisture sieving method and then detected aggregate associated organic carbon contents and bacterial communities. The results showed that: (1) regardless of the Robinia pseudoacacia plantation age, the soil aggregates were primarily macroaggregates (>0.25 mm). The proportions of macroaggregates were 92.74%-95.78% in the Robinia pseudoacacia plantations with different ages. The stability of the soil aggregates increased with plantation ages and the maximum was observed in the 30-year Robinia pseudoacacia plantations. Compared to CK, the mean weight diameter (MWD) and geometric mean diameter (GMD) in the 30-year Robinia pseudoacacia plantations significantly increased by 48.19% and 91.38%, respectively (P<0.05). (2) In the plantations of different ages, soil organic carbon contents were concentrated in the <0.25 mm fractions. Both of the organic carbon content in soil and >2 mm fractions significantly increased with plantation age. (3) The bacterial communities in different particle size aggregates were mainly composed of Proteobacteria, Actinobacteria, and Acidobacteria. During Robinia pseudoacacia growth, the relative abundances of Actinobacteria firstly elevated and afterwards reduced and the minimum was observed in the 18-year Robinia pseudoacacia plantations. The change trends of Acidobacteria were contrary to Actinobacteria. There was no obvious change of Proteobacteria. Soil organic carbon, pH, total nitrogen and phosphorus were the main factors affecting bacterial communities of aggregates. (4) In the >2 mm and 2-0.25 mm fractions, the relative abundance of Rokubacteria had the greatest impact on aggregate stability, which exerted both direct and indirect effects on aggregate stability by increasing organic carbon contents. In the <0.25 mm fractions, the organic carbon contents had the greatest impact on aggregate stability. The higher the organic carbon content, the stronger the stability of the aggregate. In conclusion, Robinia pseudoacacia plantation not only improves the stabilization of soil aggregates, but also promotes the accumulation of organic carbon, which may be used as an effective measure to restore ecology in this region. During the growing process, the plantation impacts soil aggregate stability by altering the aggregate associated bacterial community and organic carbon contents.