<p>The Qinghai-Tibet Plateau region is showing a trend of climate warming, and the active layer is thickening. The freeze–thaw (FT) cycles change the internal structure of the active layer of lateritic soil slopes, resulting in widespread landslides. At present, the research on the microstructure of Qinghai-Tibet Plateau lateritic soil under climate warming is rare. To simulate the effect of climate warming, FT tests were conducted at both fixed (F-type) and elevated (E-type) freezing temperatures. The microstructure was quantitatively analyzed using X-ray micro-computed tomography (CT), with a focus on pore structure, porosity development, and pore size distribution. Pores evolved from isolated, spherical structure into dendritic and banded structures after successive FT cycles. Surface porosity increased significantly, especially under E-type cycles, which produced a more uneven and distinct distribution due to the enhanced water migration and ice formation. For total porosity, it increased from 5.58% to 17.79% (F-type) and to 26.81% (E-type) after seven cycles. In terms of connected porosity, it rose more sharply after E-type FT tests. A log-normal distribution model was established to analyze the pore size distribution after FT tests. E-type cycles led to a more pronounced shift in the pore size distribution, characterized by a rightward displacement of the curve and a reduction in distribution width. The study shows that elevated freezing temperature FT cycles significantly enhance pore connectivity and structural damage of lateritic soil. In engineering construction in relevant areas, the effects of climate warming on the microstructural deterioration of lateritic soil should be fully considered in design and protection measures. Such consideration is essential to ensure the long-term safety and stability of engineering structures.</p>