Abstract: To address the challenges of evaluating cementing second interface bonding, specifically, the inability to integrally simulate the processes of mudcake formation, flushing, and bonding under high-temperature and high-pressure conditions, as well as measurement inaccuracies in bonding strength caused by variations in ambient temperature and humidity, a device for in-situ testing of cement sheath’s second interface bonding strength was developed, along with a corresponding testing methodology. This device enabled the integral simulation of the entire process, including simulated formation filter cake formation, flushing, cement sheath’s second interface bonding formation, and in-situ bonding strength testing under high-temperature and high-pressure conditions. With a measurement accuracy of 0.001 MPa, it resolved the issue of underestimated bonding strength results caused by filter cake drying and cracking due to temperature and humidity fluctuations. Test results demonstrate that bonding strength increases with rising formation pressure and core permeability; the material composition of different drilling fluid systems significantly influences bonding strength, and expansive cement slurry systems effectively enhance the cement sheath’s second interface bonding strength. The development of this device and the establishment of a supporting evaluation method enable accurate determination of cementing interface bonding quality and optimization of bonding performance.