Abstract：The soil shear strength is important to analyze the stability of embankment and slope. A series of soil mechanics tests(compression test，quick shear test and unconsolidated-undrained(UU) test are carried out using levee soils of downstream embankment of Yellow River，especially the strength test of the soils with different soaked periods. The change and reducing degrees of strength parameters of clay and soaked silt，and the reasons of strength change and the effect on the stability of embankment are discussed. Because of soaked soil，the compression coefficient of soil obviously increases and the modulus of compression obviously decreases. The compression coefficient of clay samples soaked for 5 days increases 1.46 times at the most than that without being soaked，and 0.64 times for silt samples. At the same time，for the soaked soil，the deformation of clay is geaterer than that of the silt. The conclusion of quick shear test is that the cohesive of clay reduces by 72.6%，silt by 62.8% and internal friction angle changes a little soaked for 5 days because the action of water to soil only destroy the sequence and cement of soil grains，but the soil grain component is not varied. The results of UU test is complex. For the clay samples，c and j decrease quickly with soaked sample，but the time effect of soaked clay is small. However，for the silt，the longer the time that the sample is soaked，the lower the strength of the silt is. It will be the reference to the design and stability analysis of embankment，and the results will be afforded for the management of the Yellow River embankment operation.
