Abstract: The strength characteristics of the unsaturated soil in Beijing area were determined by using unsaturated triaxial apparatus at different matric suctions and a quantitatire relation between strength and matric suction was established. At the same time, we carried out a test of influence water content on the strength of the unsaturated soil. The result shows that the strength is raised at the different matric suctions and the change of water content obviously influences the cohesive force, but not remarkably influences the internal friction angle. We measured the turning point of water content to the strength changes of these specimens too.