To reveal the shear mechanical characteristics of the interface between deep alluvium frozen/thawed soil and concrete structure, a series of direct shear tests were carried out under high normal stress and thawing condition by using an improved DRS-1 high pressure direct/residual shear test system. Basic shear mechanical characteristics of the interface between frozen/thawed soil and structure were summarized. Based on the test results, empirical equations of shear stress-strain relation of interface between frozen/thawed soil and structure under different high normal stress and thawing conditions were established, considering pre-peak stress and strain softening behavior, respectively. Effects of normal stress and thawing degree on the maximum shear stress and the initial shear modulus were discussed. Results show that the pattern of shear stress-strain curves transformed gradually from strain softening to strain hardening as the process of thawing. When the shear strain was small (pre-peak), the general hyperbolic model could reasonably describe the shear stress-strain relation of the frozen/thawed soil-structure interface. Furthermore, an improved hyperbolic model in consideration of strain softening behavior was proposed to describe the whole shearing process under different high normal stress and thawing conditions.