[Objective] Studying the quantitative relationship between soil boundary water content and mechanical composition of dolomite slope farmland in Central Guizhou Province, which provided scientific basis for the study of soil erosion process mechanism of sloping farmland in this area.[Methods] Field sampling, laboratory test and analysis by SPSS software.[Results] In the dolomite area of the slope farmland, the relationship of the plastic limit with the soil clay content, powder content and fine sand content has a positive correlation, but has a negative correlation with the content of coarse sand; the soil liquid limit increases with the increase of soil clay content, but reduces with the increase of coarse sand. The soil liquid index was positively correlated with soil clay content, but negatively correlated with coarse sand content, and there is no significant correlation between the soil mechanical composition and the plastic index of the soil.[Conclusion] The soil mechanical composition of the slope farmland in dolomite area of Central Guizhou Provinceis closely related to the limit water content, the soil moisture content can be obtained by soil mechanical composition.