Abstract: In order to study the deformation and triaxial strength behaviors of frozen loess and frozen-improved loess, a series of triaxial compression tests are conducted under confining pressure varying from 1 to 15 MPa at -6 °C. The results show that the shape of stress-strain curves presents strain softening and strain hardening successively. Both the initial tangent modulus and the volumetric strain increase at first then decrease with the increase of confining pressure. The triaxial strength of frozen loess and frozen-improved loess increases at first then decreases with the increase of confining pressure. The strength of frozen loess is enhanced after being improved, and the improvement effect of cement is more significant. Based on the Mohr-Coulomb criterion, the variation laws of generalized cohesion and internal friction angle with confining pressures of frozen loess and frozen-improved loess are obtained. Meanwhile, a nonlinear Mohr-Coulomb strength criterion for frozen loess and frozen-improved loess is proposed, which reflects the phenomenon that the triaxial strength changes nonlinearly with the increase of the confining pressure.