Abstract: Through soil investigation developed from several important ground substance,using the methods of statistics analysis,the paper studies the relationship between ground substances and soil mechanical composition.Results show that ground substances significantly affect soil mechanical or physical composition and that there are significant differences among soils developed from different ground substances such as rock fragment content,sand grain ratio and clay ratio.As a whole,the soil developed from carbonatite group has lower sand grain ratio(17.84%) but higher silt ratio(43.93%) and higher clay ratio(38.24%).The soils developed from purple sand-shale and sand-shale have higher sand grain ratio and lower clay ratio.Soil developed from coal series has similar character to carbonatite soil and soil from slate has moderate mechanical composition.The conclusion could provide the theory foundation for soil erosion research in Guizhou Province.