Abstract: In order to verify the reasonableness of two stress state variables for unsaturated soils and to improve the accuracy of tests, the triaxial apparatus for conventional unsaturated soils has been improved to control the pore water pressure, the inner and outer chamber pressures with three pressure-volume controllers. Using the improved triaxial apparatus, the equal cell pressure compressed tests on remoulded and undisturbed Q₃ loess with different initial dry densities, initial saturations and initial suction is are performed to verify the reasonableness of two stress state variables for unsaturated soils. In the tests, the confining pressure, pore water pressure and pore gas pressure equivalently change while the stress state variables themselves do not change, and then, by the amount of the change of volume and moisture content of samples to verify the reasonableness of the two stress state variables for unsaturated soils. The results show that for the remoulded and undisturbed Q₃ loess, only change the individual components of the stress state variables while the stress state variables themselves do not change, can the change of volume and moisture content of samples be ignored. It is reasonable to describe the mechanical behavior of unsaturated soils by using the two stress state variables, and it gives a large number of experimental data to the theory of two stress state variables for unsaturated soils.