[Objective] The characteristics of soil aggregates under different vegetation types and slope positions of Culai Mountain were determined in order to provide theoretical support for vegetation construction and soil and water conservation in rocky mountain areas of North China. [Methods] The composition and stability of soil aggregates on and below the slope of Robinnia pseudoacacia×Quercus mixed forest and Chestnut forest of Culai Mountain were analyzed by dry sieve and wet sieve methods, and the soil solid-liquid-gas three phase rate and its structural distance were measured. [Results] ① The composition of mechanically stable aggregates accounted for 55.60%-72.76% for particle sizes of 2-0.25 mm, 25.11%-41.98% for particle sizes of 0.25-0.053 mm, and 0.60%-3.75% for particle sizes ＜0.053 mm. ② Compared with the Chestnut forest, the mean weight diameter of soil mechanical stability aggregates increased by 10.51%, geometric mean diameter increased by 7.51%, and unstable aggregate index decreased by 19.01% in the Robinia pseudoacacia and Quercus mixed forest. However, none of the indexes of water stabile aggregates showed significant differences under different vegetation types and slope positions. ③ Soil solid phase volume (56.46%-66.15%)＞liquid phase volume (21.66%-36.56%)＞gas phase volume (4.40%-12.19%). The soil three phase structure distance of Robinia pseudoacacia and Quercus mixed forest was reduced by 8.87% compared with that of Chestnut forest. [Conclusion] The influence of vegetation type on the structural stability of soil aggregates of Culai Mountain was greater than that of slope position, where the contribution of Robinia pseudoacacia and Quercus mixed forest to the mechanical stability of soil aggregates was significantly greater than that of Chestnut forest. The solid volume ratio was the key factor explaining the composition of soil aggregates.