The effects of different crop straw returning modes on the particle size composition of stable soil aggregates under wheat-maize rotation were studied. The results showed that under the condition of no straw returning measures, the percentage of silt（2～20 μ m） in soil was the highest（54.41 ±2.87）%, while wheat returning could increase sand content by 38.90%, decrease silt content by 24.53% and clay content by 14.37%, and can enhance soil resistance to erosion. However, the fertilizer and maize straw returning had little effect on soil aggregate stability.