Bi-metallic mechanical clad pipes are one of the main measures for anti-corrosion control of oil and gas field gathering and transmission pipelines. The failure of their liner layers restricts the clad pipes' engineering application. In order to explore the buckling failure mechanism of liner layers of bi-metallic mechanical clad pipes, the mechanical model of a clad pipe under bending load was established. The influence of forming pressure, working pressure and composite pipe structural parameters on the failure mode of the liner layer lining was studied. The results show that the buckling resistance of the liner layer is improved by increasing the residual contact pressure. The buckling time of the liner layer is delayed and the fold amplitude is reduced by increasing the working pressure. The reduction of the initial layers gap of the clad pipe before forming is beneficial to improve the buckling resistance of the liner layer. With the increase of the wall thickness of the outer base pipe, the wall thickness of the lining pipe and inner diameter of the clad pipe, the buckling resistance of the lining pipe increases.