Abstract：A series of triaxial shear tests with controlled suction and net constant confining pressure and the tests with controlled water content and constant confining pressure were conducted to study the effects of deformation，strength and yield properties of unsaturated undisturbed loess Q2 with suctions or initial water contents. The test results show that the failure model of unsaturated undisturbed loess Q2 with controlled suctions equaling 100，300 and 450 kPa is shown with plastic failure；but the failure model of unsaturated undisturbed loess Q2 with controlled initial water contents equaling 4.78% and 7.64%，respectively，is displayed with brittle failure. The stress-strain curves of undisturbed loess Q2 will change from strain softening to strain hardening with the decrease of suction(or the increase of water content) and the increase of consolidation cell pressure. The cohesion of unsaturated undisturbed loess Q2 has a linear increase with the increase of suction within research suction range(100–450 kPa)，but the friction angle is found to have little change with the change of suction. A new method to identify the field stress of undisturbed loess Q2 under triaxial shear condition is suggested. The net mean yield stress and deviatoric yield stress both increase with suction，where the deviatoric yield stress has a linear increase with net mean yield stress under the same suction or water content.
