Abstract: During the steam huff and puff process (300～350 ℃) of heavy oil thermal recovery wells, the application of insulated tubing reduces radial heat loss. However, the temperature of the wellhead cement sheath system still remains in the range of 150～200 ℃, leading to thermal cycling that impairs the integrity of the cement sheath interface. Aiming at the typical service conditions of heavy oil thermal recovery wells, a radial stress monitoring device for the cement sheath interface was employed to monitor the radial stress of the cement sheath interface under thermal cycling, thereby obtaining the critical temperature difference-stress parameters for the initiation of cement sheath interface failure under thermal cycling. Based on elastic-plastic theory, an elastic-plastic mechanical model of the cement sheath system under temperature-pressure coupling was established, which reveals the failure mechanism of the cement sheath interface. Experimental results demonstrate that the inconsistent thermal expansion between the casing and the cement sheath under thermal cycling results in uncoordinated interface deformation. This causes the radial compressive stress at the cement sheath interface to convert to radial tensile stress during temperature difference unloading, leading to interface bonding failure and the formation of micro-annuli. Theoretical analysis indicates that the accumulated plastic deformation of the cement sheath under thermal cycling is the primary cause of the generation of radial tensile stress at the interface and subsequent bonding failure, the law of mechanical and thermodynamic parameters of the cement sheath on interface integrity is clarified. The research results can provide a theoretical basis and technical reference for the optimal design of drilling and completion engineering for heavy oil thermal recovery wells.