Abstract: This paper investigates the effect of matric suction on the shear strength and deformation mechanical properties of unsaturated sliding-zone soil. It uses the undisturbed sliding-zone soil samples from the Huangtupo riverside slump-mass No. I for the tests. A series of consolidated drained direct shear tests are carried out under different combination of net normal stresses and matric suctions with GDS direct shear system. The experimental results show that an increase in net normal stress results in a higher shear strength under constant matric suction conditions. The stress-strain curve appears strain-hardening behavior as net normal stress increases when matric suction is 50kPa. As matric suction increases and exceeds net normal stress, the stress-strain curve appears a peak shear strength followed by a strain-softening behavior apparently. Or the stress-strain curve appears strain-hardening behavior. Under constant net normal stress conditions, an increase in matric suction results in a higher shear strength. The stress-strain curve changes from a peak shear strength followed by a strain-softening behavior under lower normal stress to a strain-hardening behavior under higher normal stress. The vertical displacement during shearing appears shear dilation when matric suction is greater than net normal stress. Otherwise, the curve appears shear compression. Under consolidation and drain condition, the cohesion of sliding-zone soil increases with matric suction linearly. The unsaturated shear coefficient b is calculated to be 13.7according to the relationship between cohesion versus matric suction. The effective friction angle increases with matric suction slightly. The average effective friction angle is 15.9.