This study applied Time Domain Reflectometry (TDR) technology to quantify the deformation of coaxial cables with shear and extension in the laboratory by simulating the type and magnitude of cable deformation in a landslide. First, the test simulated two sliding planes by shear displacement in the laboratory with a TDR coaxial cable. Then, a TDR tester interrogated the reflected V-type waveforms of the cable. Subsequently, a quadratic regression established the relationship between reflection coefficient integrals and deformation magnitude. The maximum magnitude of a cable deformation by shearing was approximately 60 mm. Therefore, the changes of the cable's shear deformation can be determined using the regression equation. The second test was an extension with the TDR technology. The result of reflected waveforms illustrated a significant increase in the amplitude of reflection coefficient as the cable ruptured, and the maximum magnitude of the cable’s extension displacement was approximately 40 mm.