[Objective] Proportion and stability of soil aggregates are important factors affecting healthy and sustainable development of paddy soil. [Method] A long-term stationary experiment on effects of crop rotation systems, including multi cropping, crop rotation and winter fallow, on paddy field was carried out in the years from 2012 to 2017. The experiment was designed to have five treatments: Double-cropping rice plus winter fallow land, double-cropping rice plus milk vetch in winter, double-cropping rice plus canola in winter, double-cropping rice plus garlic in winter and double-cropping rice plus ?. Soil samples were collected from the 0~50 cm soil layers of the plots of the five treatments for analysis, using the wet screening method, of proportions of the aggregates, 1 ~ 2 mm, 0.5 ~ 1 mm, 0.25 ~ 0.5 mm and 0.25 mm in particle size, separately and then, mean weight diameter (MWD), mean geometric diameter (GMD) and fractal dimension (D) of the fractions of soil aggregates was calculated, separately. [Result] Results show that regardless of treatment, the soil aggregates in the 0~50 cm soil layer were dominated with the fractions of 0.25 ~ 0.25 mm and < 0.25 mm in the time periods after the early or the late rice was harvested, and the two fractions reached 78.1% ~ 84.8% and 85.6% ~ 91.1%, separately, in cumulative content, while the fraction of aggregates of 1 ~ 2 mm and 0.5~1 mm, was only 13.1% ~ 21.9% and 8.9% ~ 14.4%, respectively. Obviously the cultivation of early and late rice increased the fractions (>0.25), but reduced those (< 0.25mm), and the effect of early rice was more prominent than that of late rice. The two crops also affected MWD and GMD significantly, but not D. [Conclusion] It is, therefore, quite obvious that the systems of multiple cropping rotations and two crops of rice plus straw returning are favorable to formation of large-sized aggregates rather than fine aggregates and the effect of increasing water-stable aggregates is more significant with early rice than with late rice, which in turn improves yield of the two crops. All the findings in this experiment are of great significance to the sustainable development of rice production in South China.