Abstract: The mineral composition of the PRD's soft clay was analyzed quantitatively by using the X-ray diffraction method, and the total specific surface area of artificial soil samples and natural soil samples was tested by EGME method for studying the influence of mineral composition to the soil's strength characteristics.It is found that clay mineral(such as montmorillonite) is usually lamellar particle, has a lareg specific surface area, the adsorptive bound water membrane is thicker, intergranular direct contact between particles is less, the cementing actions connected by the combined water film is more obvious, and lubrication friction is formed intergranulas due to easy movement, which can be expressed by the lower shear strength and smaller angle of internal friction and the high cohesive force.And non-clay mineral particles(such as quartz) are usually granular or needle, specific surface area is small, adsorbed water film is thinner, cohesive force is low, and there is a direct contact with the friction angle between particles, so as to increase its strength.