Abstract: The slope surface deformation and displacement are related to the precipitation. The root cause is volumetric strain caused by suction decreasing in unsaturated soils. By simply increasing the suction stress path, under net confining pressure of 100kPa or 200kPa, the test of volumetric strain due to suction is done on undisturbed landslide samples and its remolded sample. The results show: (1)The volumetric strain of the specimen monotonically increases with suction increasing, which obeys logarithm function relation; (2)Bulk modulus during net confining pressure from 100kPa to 200kPa, monotonically increases with suction increasing, which obeys the power function relationship; (3)Coefficient of volume change associated with the suction monotonically decreases with suction increasing, which obeys the power function relationship. When the suction is greater than 200kPa, with the suction increases, the volume change of coefficients is close to a constant of about 0.0059. Based on these results, the pattern and mechanics of volumetric strain caused by a simple suction change are discussed in this paper.