<p>The issue of cement sheath sealing failure hinders the development of coalbed methane (CBM). The direct cause of cement sheath sealing failure is damage at the cement sheath interface, but the specific failure modes remain unclear and require targeted research. This study establishes a casing-cement sheath-formation assembly model for CBM wells and uses numerical simulation methods to investigate the effects of wellbore pressure changes during actual fracturing operations on the assembly. The stress-strain distribution on the wellbore wall and cement sheath bonding interface, as well as the displacement distribution of the casing-cement sheath-formation assembly during fracturing, are analyzed. Combined with the simulation results of interface integrity, the failure characteristics of the cement sheath bonding interface in CBM wells are identified. The redistribution of stress states in the casing-cement sheath-formation assembly caused by wellbore pressure changes, along with the combined effects of operational pressure and in-situ stress, leads to elliptical deformation of the casing. During fracturing, the strain in the assembly is minimal, and the bonding interface is damaged due to internal stress changes in the assembly. After the pressure testing phase, large-scale failure occurs in the casing-cement sheath interface outside the maximum principal stress direction and in the cement sheath-formation interface outside the minimum principal stress direction. The failure mode of the bonding interface is shear failure. The research results contribute to understanding the failure modes of the cement sheath bonding interface in CBM wells and provide guidance for optimizing cement sheath parameters.</p>