Slope cropland of purple soil was the main part of agricultural production in the hilly region of Sichuan basin, where there are large precipitation and concentration in summer and autumn. When the rainstorm occurred, the water and soil loses easily, which led to shallowing soil layer, decreasing the soil moisture and seasonal drought occurrence. Some researchers found that the straw, the biochar and the organic fertilizer were able to increase the soil porosity and enlarge the soil moisture, but there was rare in the slope cropland of purple soil. Thus, to investigate the effect of soil ameliorants on the composition and stability of soil aggregate and moisture storage capacity of slope cropland in purple hilly area, two-year filed experiment was conducted by employing five kinds of soil ameliorants including straw, organic fertilizer, biochar, carbonaceous ameliorant I and Ⅱ. The results showed that all these five carbonaceous ameliorants were also observed to have the ability on enhancing the sequestration and storage of soil for precipitation, which could further markedly increase the saturated soil moisture content and maximum effective water and flood detention storage and decrease the water content of wilting point. The effect of these five soil ameliorants on the maximum effective capacity followed the trend: Carbonaceous ameliorant Ⅱ>carbonaceous ameliorant I>biochar>manure>straw>CK. The soil bulk density and soil porosity also received valid improvement after applying these ameliorants (besides straw), which significantly decreased and increased, respectively. In addition, the mechanical stability and the water stable aggregate content of soil with particle size >0.25mm significantly increased after soil ameliorants applied, while the micro-aggregate (<0.25mm) content decreased, suggested that the soil ameliorant could promote the conversion of small aggregate to large aggregate with the best promotion observed for >5mm particle (increased 14.5 to 60.7% compared with the contrast). Employing these soil ameliorants had obvious effect (followed the trend: carbonaceous ameliorant I≈carbonaceous ameliorant Ⅱ>biochar>organic fertilizer>straw>control) on increasing the average weight diameter and stability index of aggregate. Correlative analysis showed that there was a positive correlation between total storage capacity, active storage capacity, flood detention storage capacity and total soil porosity, capillary porosity, content of large aggregate, and there was negative correlation with non-capillary porosity and content of small aggregate. Therefore, there was close relation between soil moisture preservation and soil porosity. Applying soil carbonaceous ameliorant was an important measure to improve the structure of purple soil and increase the ability of moisture holding and anti-erosion of purple sloping cropland by promoting the conversion of small aggregate to large one, decreasing the soil bulk density, increasing the soil porosity and enlarging the soil moisture holding and the soil effective water storage, which prevented sloping land from the damage of local seasonal drought. Moreover, the limiting factor of low soil moisture preservation in slope cropland of purple hilly area might be low organic matter content.