Abstract: The characteristics of anisotropy are considered to have important implications for stability evaluations of soft clay. A new type of test device and test method for in-situ anisotropy testing of soil are proposed, and the formulas of strength in the horizontal and vertical directions are given. In-situ shear tests of soft clay were conducted, to test the horizontal strength and vertical strength, as well as anisotropy ratio of soft clay. Meanwhile, the test result was used in the slope stability analysis. The results indicated that it is applicable to use the "double-vane" shear test to measure the horizontal strength and vertical strength of soft clay, the value of anisotropy ratio S_h/S_v is bigger than 1. And it is more reasonable to take account of anisotropy ratio into the slope stability analysis of soft clay.