Abstract: To study the variation of matric suction and shear strength of unsaturated soils with different water contents,a group of tests were performed to measure the strength of expensive soil during a cycle of desorption-absorption of moisture.Desorption-absorption of moisture was achieved by controlling the suction at different levels.Direct shear tests were conducted to measure strengths of soil samples with controlled suctions in the desorption or absorption process of moisture.From the test results,we could get some insights that:①soil-water characteristic curve of soil was unstable and related to the variation of soil moisture;②different variation of soil moisture might lead to different contribution of the same suction to the strength of soil.