In this study, PAM, humic acid, chitosan and aluminum sulfate were used as soil cementing materials to research the processes and effects on the formation of large aggregates from ＜0.25 mm aggregates in the loessial soil. The results showed that: (1) Based on the analyses of soil particle size distribution, soil cementing materials used in this study were all beneficial for formation of ＞2 mm aggregates, especially for ＞5 mm aggregates. (2) All of these four cementing materials could effectively increase the mean weight diameter and mean geometric diameter of the loessial soil, and the enhance the stability of aggregates, which increased with the increasing application rate of the cementing material. (3) Different soil cementing materials had different ability to improve soil structure, and showed the order of PAM≈humic acid＞chitosan＞aluminum sulfate. The findings obtained from this work will provide theoretical supports for application soil cementing materials to improve soil structure scientifically．