【Objective】We aimed to study the effects of litterfalls and earthworms on the distribution of soil aggregates and the contents of carbon and nitrogen in aggregates of different particle sizes, and to reveal the distribution of soil aggregates and the changes of organic carbon and total nitrogen in aggregates. 【Method】 We set up the field fixed experimental plots using a random block experimental design in a poplar plantation located along the coast of Dongtai City, Jiangsu Province, China. A total of six different treatments were used, namely, a control treatment (CK), a poplar leaf litter surface application treatment (T1), a poplar leaf litter mixed application treatment (T2), an earthworm inoculation only treatment (T3), a poplar leaf litter surface application and inoculated with the earthworm treatment (T4), and a poplar leaf litter mixed application and inoculated with the earthworm treatment (T5). Four replicate plots were set for each treatment. According to the different particle sizes, the aggregates in the soil were graded, and the organic carbon and total nitrogen content of each particle size aggregate were determined. At the same time, the mean of weight diameter (MWD) was used as an indicator of the stability of the aggregates. 【Result】The organic carbon content of water-stable aggregates with different particle sizes generally increased with particle sizes. The organic carbon content of aggregates increased more in the T5 group than that in the T4 group. Furthermore, both the surface application and the mixture application of poplar leaf litter can increase the organic carbon content of aggregates with different particle sizes. Compared with the total nitrogen content of different particle size aggregates in the same treatment, the total nitrogen content of aggregates with particle sizes of ≥0.250-2.000 mm is generally higher than those of the other particles, while the total nitrogen content of aggregates with a particle size of ﹤0.053 mm was the lowest. 【Conclusion】The earthworm inoculation could improve the total nitrogen content of soil aggregates in the poplar plantation, and the mixed application of poplar leaf litter could improve the total nitrogen content of soil aggregates more effectively than the surface application. This study also showed that the earthworm inoculation accelerated the humification process of the soil organic matter in a poplar plantation and accelerated the decomposition rate of soil organic matter. In addition, compared with the surface application of poplar leaf litter, the mixed application of poplar leaf litter will also accelerate the humification rate and the decomposition of the soil organic matter.