Abstract: Through the triaxial CD tests of compacted silts under controlled matric suction by using an unsaturated GDS triaxial apparatus,the mechanics property of the silts was analyzed,and the influence of matric suction was taken into consideration.Resultsshow that the influence of matric suction on the suction friction angle(b) of unsaturated compacted silts is significant,but on the effective cohesive strength and friction angle are small; increasing of matric suction advances the soils' capacity of shear resistance under the same net cell pressure; the similar stress and strain curves are observed on the soil with the different suctions,and the curve form is mainly affected by the soil composition,structure and its stress history other than water content or suction; according to the good power relationship existing in the suction of unsaturated soil and the adsorption strength,the shear strength formal proposed by Fredlund can be modified into the formula taken suction as direct variable.