Abstract: To study the strength and yield characteristics of cinder-improved soil, the triaxial tests under different freeze-thaw cycles were carried out. The influence of mix proportion and freeze-thaw cycles on the strength characteris- tics and yield surface of cinder-improved soil were obtained through the tests. The expression of yield surface was mod- ified by introducing the influence factor of mix proportion and freeze-thaw cycles,and the double yield constitutive re- lation of improved soil was obtained. The results show that with the increase of cinder content,the cohesion of the im- proved soil increases first and then decreases,the internal friction angle increases slightly. Shear strain yield surface and volumetric strain yield surface exhibit the rule of first expansion and then shrinkage. With the increase of freeze- thaw cycles,the cohesion of the improved soil decreases obviously,while the internal friction angle changes little. Shear strain yield surface and volumetric strain yield surface gradually shrink to the origin with the increase of freeze-thaw cycles. The influence factors of mix proportion and freeze-thaw cycles can better reflect the evolution of the yield sur- face of the improved soil. The constitutive relationship based on the results has a better accuracy.