Abstract: Next-generation large-scale lightweight aircraft experience more significant cumulative thermal deformation during prolonged high-speed flight than conventional aircraft, adversely affecting flight performance. Focusing on typical high-aspect-ratio cavity plate structures, this study adopted a high-fidelity fully numerical aero-thermal-structural coupled analysis method to investigate: (1) structural deformation evolution under coupled aerodynamic heating and loading, (2) thermal-mechanical interaction mechanisms, and (3) deformation effects on flight performance. The results showed that under prolonged severe heating conditions, the thermal deformation of cavity structures was determined by the combined effects of time-accumulated thermal factors and instantaneous mechanical loads, exhibiting three distinct evolutionary stages: Stage I (rapid deformation dominated by cold-wall heating), Stage II (gradual deformation increase followed by recession under continued aerodynamic heating), and Stage III (stabilized deformation through thermal-mechanical equilibrium). Unlike solid structures, cavity structures demonstrated this unique recession behavior consistently across different Mach numbers and angles of attack. The cumulative thermal deformation caused nonlinear variations in aerodynamic characteristics throughout the flight, leading to adverse effects such as deviations in lift-to-drag ratios and pitching moments. These findings highlight the need to address such thermal deformation effects in the design of future high-speed aircraft.