A series of hollow cylinder torsion shear tests were conducted for the silty soil in the Yellow River flood area, considering the effect of drainage shearing with fixed large principal stress direction. The shear stress-strain behavior as well as the anisotropy characteristics of silty soil were then presented. Under different intermediate principal stress coefficient b and major principal stress direction angle α, the stress-strain relationship and the corresponding shear stress ratio of silty soil were obtained. It was concluded that the value of and have a significant effect on the octahedral stress-strain and the shear stress-major principal strain. The obvious anisotropic character was observed, especially under or 1. Compressed deformation usually occurred in the major principal strain direction. Under a fixed α, the smaller shear strength occurred under a larger value. The peak shear strength and the corresponding axial strain were the largest under the conditions of α=45° and b=0.5, corresponding to the largest