Abstract: Based on the example of cubic loose accumulation, a quantitative relation expression is deduced theoretically between wet suction and water content of unsaturated soils. The suction tests on remodeling fine grain sand soil with different water content are carried out, and a curve-fitting of the test results is analyzed. Theoretical calculations and experimental results show that for specific unsaturated soils, with the increase of the water content, the suction wet increases first and then decreases, which is the same as that when there is a certain boundary of water content. This agrees with the fact that in a certain range, the strength of the unsaturated soils, especially the unsaturated sand soils, increases first and then decreases with the increase of the water content. It indicates that the wet suction, instead of matrix suction, is the important part of effective stress.