<p>Pipeline-soil coupling numerical model was established to investigate the mechanical behavior and interfacial separation of X65/316 L bimetallic composite pipelines under reverse fault displacement, the effects of fault displacement, soil elastic modulus, and forming gap on mechanical response and interfacial delamination were analyzed. The results demonstrate that the stress, strain, and radial relative displacement on both the left and right sides of the fault exhibit distinct variation patterns under different parameters. Specifically, larger fault displacements lead to increased stress, strain, and radial relative displacement at both the top and bottom of the inner pipeline. A lower soil elastic modulus (e.g., decreasing from 15 MPa to 10 MPa) significantly increases the pipeline stress by approximately 100 MPa, while a higher soil elastic modulus amplifies the maximum compressive strain and radial relative displacement at the top and bottom of the inner pipeline. Although the forming gap has minimal influence on the stress at the top of the inner pipeline, increasing the gap from 1.5 mm to 2.0 mm reduces the strain at the bottom by a factor of 9.57. Furthermore, increasing forming gap substantially enhances the compressive strain at both the top and bottom of the inner pipeline but has a limited effect on the radial relative displacement. This study presents the first investigation into the mechanical behavior and interfacial separation of bimetallic composite pipes under reverse fault motion, systematically examining their evolution mechanisms under various parameters. The results can provide design guidance and safety assessment for bimetallic composite pipeline.</p>