<p>Microwave processing is a promising postharvest technology for producing shelf-stable products from heat-sensitive agricultural commodities. However, inherent non-uniform heating often leads to structural collapse and quality degradation. During dehydration, uneven heating induces heterogeneous tissue responses, which in turn alter moisture transport and the redistribution of bioactive compounds. To address these issues, this study established a synergistic strategy by integrating ultrasound–emulsion pretreatment (UE) with microwave vacuum drying (MVD). The investigation focused on drying kinetics, regional responses of dielectric and thermal fields, and microstructural evolution to elucidate the coupling behavior between heat–mass transfer and quality changes. The results demonstrated that UE-MVD markedly improved both drying efficiency and structural stability. The effective moisture diffusivity of the UE-MV_-80D group reached 1.25 × 10⁻⁷ m²/s, representing a 26.08% increase compared with the control. UE pretreatment enhanced dielectric–thermal uniformity by improving the spatial distribution of dielectric constant (<i>ε</i>′) and dielectric loss factor (<i>ε</i>″) and reducing tan<i>δ</i> gradients, thereby facilitating more homogeneous volumetric heating. In terms of product quality, <i>β</i>-carotene content was retained at 0.90&#xa0;mg/g (dry weight, DW), 38.81% higher than the control, while sugars and other thermolabile compounds were also better preserved. Correlation analysis further revealed a strong association between <i>β</i>-carotene content and <i>L</i>^*, <i>a</i>^*, and <i>b</i>^* values, highlighting its pivotal role in color formation. Overall, this work demonstrates that enhancing field uniformity can regulate membrane-associated mass transfer, providing theoretical guidance for the gentle and uniform microwave drying of thermosensitive, bioactive-rich products.</p> Graphical Abstract <p></p>