Abstract: Copper water-stop is the most important waterproofing component between joints in hydraulic concrete structures. Concrete structure often experience uneven deformation under the action of gravity and hydrostatic pressure, resulting in tension (compression), settlement, and shear deformation (relative displacement) between the two wings of copper water-stop. The safety of copper water-stop depends on the value of the three-dimensional deformation, which is often judged by the displacement in three directions separately, without considering the coupling effect of three-dimensional displacement. In this paper, a total of 40 copper water-stop specimens of two sizes were designed and produced. Shear tests under different tensile and settlement displacement were conducted with these copper water-stops using a test platform that allows independent control of three directions. The shear deformation law and failure mode of copper water-stops were studied, and the failure envelope surface in the three-dimensional displacement space was obtained. A deformation and failure criterion for copper water-stop under three-dimensional displacement conditions was proposed, which can be used to judge the safety of similar copper water-stops.