Abstract: Under controlled suction conditions, CD shear tests were conducted using a modified triaxial shear apparatus on dynamic compacted unsaturated silt from the foundation of the Local-Tax Building in Shijiazhuang city, China. The test results clearly demonstrated that suction severely influences the shear strength of the soil. The relationships of the effective cohesion and the friction angle to the suction are well linear. The effective cohesion increases and the friction angle decreases with increasing suction. In a given suction range, the influence of the suction on the effective cohesion is more evident than the friction angle. The failure envelope of the compacted silt is not a plane, which shows convergent with increasing the net average stress and the suction. When the confining pressure is higher than 300 kPa, it plays the leading role on strength, not the suction.