<p>The thrust chamber is a critical yet vulnerable component of liquid rocket engines, with the "dog-house" failure mechanism on its inner wall constituting a primary constraint for enhancing engine life. The sandwich beam theory serves as a classical framework for predicting the service life of thrust chamber's inner wall, enabling the characterization of inner wall's damage and thinning as continuous temporal functions. Based on the concept of the sandwich beam model, this study independently establishes an improved sandwich beam model and presents a detailed derivation process. The improved model considers the existence of the cooling channel fillets, and is suitable for the case that the thermal strain difference of the cold and hot wall surfaces changes along the circumference, which better aligns with the physical and engineering practice. The calculation result shows that the introduction of the fillets, while improving the stress concentration, will lead to a reduction in the service life of the inner wall. Therefore, the fillet radius should not be too large. Comparative analyses between thinning models based on linear deflection distribution and arc-shaped deflection distribution were conducted, leading to the establishment of an optimized thinning model for inner wall with fillets. The model considers the influence of fillet radius and plastic compression effect on the thinning amount, and improves the reliability of life prediction. Finally, the improved model combined with creep constitutive relation was used to calculate the damage and life of the thrust chamber's inner wall, and the influencing factors of life were analyzed. This research provides valuable theoretical references for thrust chamber's life prediction and real-time damage assessment, while also offering conceptual foundations for offline damage mitigation control system design.</p>