Abstract: To address the challenges in evaluating the cement bond at the second interface—specifically, the inability to integrate the simulation of filter cake formation, displacement, and cement bonding under high-temperature and high-pressure conditions, as well as the inaccuracies in bond strength measurements caused by variations in temperature and humidity—a new in-situ testing device for measuring the cement bond strength at the second interface was developed, along with a corresponding testing method. This device enables the integrated simulation of the entire process under high-temperature and high-pressure conditions, including filter cake formation, displacement, cement bond formation at the second interface, and in-situ bond strength testing, with a measurement accuracy of 0.001 MPa. It effectively resolves the issue of underestimating bond strength due to filter cake cracking caused by changes in temperature and humidity. Test results demonstrate that bond strength increases with higher formation pressure and greater core permeability, the material composition of different drilling fluid types significantly influences bond strength, and expansive cement slurry systems effectively enhance the cement bond strength at the second interface. The development of this device and the establishment of supporting evaluation methods enable accurate measurement of the cement bond quality and effective optimization of cementing performance at the interface.