Abstract: In the seasonal frozen soil area, periodic freeze-thaw action has continually changed micro-structure and physical-mechanical properties of shallow unsaturated soil, which has directly affected the interaction between soil and structure. The stress-strain relation and strength characteristics of the interface between soil and structure are the bases and keys to determine the bearing capacity and security of foundation engineering, and to analyze the interaction between structure and soil in seasonal frozen soil regions. In order to provide the practical engineering with better services, the stress-strain curve and the interface strength parameter changing with the number of freeze-thaw cycles under different experimental conditions are obtained from the direct shear test of unsaturated loess-concrete samples with different water contents and different freeze-thaw cycles. Correspondingly, the matrix suction of the loess under the same experimental conditions is tested using filter paper method. Moreover, the constitutive model of shear stress and displacement as well as freeze-thaw cycle in the loess-concrete interface is established with experimental data, which has a good description of the relationship between shear stress and displacement of the loess-concrete interface under different pressure after several freeze-thaw cycles. Also, the research results will provide reference for the numerical calculation of the foundation bearing capacity in the seasonal frozen soil area.