The rotary air preheater plays a crucial role in recovering waste heat from the boiler, but its efficiency is significantly affected by air leakage, especially during deep peak-shaving operation, where rotor thermal deformation leads to prominent radial air leakage issues. To address this, a thermo-fluid-solid coupled computational model is proposed, which incorporates the rotor's “mushroom-shaped” thermal deformation characteristics to accurately simulate the leakage behavior induced by thermal deformation. The study primarily analyzes the impact of rotor thermal deformation on the sealing gap and leakage rate. Under boiler maximum continuous rating (BMCR) conditions, the model results show that hot-end leakage accounts for 78.75% of the total leakage. When the reserved clearance is increased to 25 mm, the leakage rate can reach up to 39.8 kg/s. For every 1% increase in leakage rate, an additional 2 102.9 tons of standard coal are consumed annually, and the model's prediction results are consistent with the actual data of the power plant. The study demonstrates that incorporating thermal deformation effects into the analysis of air leakage significantly improves the model's predictive accuracy for leakage distribution under different unit clearances. This research provides theoretical support for optimizing the sealing system design of the rotary air preheater and offers practical solutions for enhancing operational efficiency and reducing energy consumption.