In order to explore the relationships between soil water dynamics and aggregate stability under different vegetation cover, the soil under the three vegetation types of osmanthus field, rapeseed field and fir field was selected as the research objects. The relationships between soil aggregate and soil water content in the long-term, short-term (before and after short-term rainfall) were investigated. The results showed that in the relatively long-term (one year), the aggregate stability under the fir trees field was significantly higher than those of the osmanthus and rapeseed fields. The water stable aggregate was dominated by 0.25~2 mm. The one-year aggregate variation was significantly negatively correlated with soil water content, which meant the aggregate stability increased with decreasing soil water content. For example, in osmanthus field and rapeseed field, soil water were positively correlated with the portion of aggregate (< 0.25 mm), but negatively correlated with the portion of aggregate (> 0.25 mm). This indicated that the soil water content could promote the large aggregates into microaggregates, and therefore, the stability of aggregate changed. In the short term, the soil aggregate mean weight diameter (MWD) changed in response to the soil water content.Specifically, soil aggregate MWD showed a downward trend with the beginning of rainfall, then reached a minimum value, after that, the aggregate MWD rose gradually when the rainfall stopped. The pattern of aggregate MWD was related with the rapid changes in soil water caused by rainfall and rainfall mechanical effect. Therefore, in combination with long-term and short-term changes of aggregate, fir trees in red soils can effectively regulate the dynamics of soil water variation, and improve the stability of aggregates, then play important role in preventing soil water erosion.