Global warming is increasing the frequency and severity of heatwaves worldwide, but their local expression is strongly modulated across hydroclimatic transition zones along arid-humid gradients. The Loess Plateau-Qinling Mountains region, a major transition zone in Eurasia, offers a natural setting for examining differentiated heatwave dynamics. Using high-resolution climate datasets and extensive station observations, we analyzed daytime, nighttime, and compound heatwaves during 1979-2023, and confirmed that ERA5 was consistent with station observations. Daytime, nighttime, and compound heatwaves increased by 0.13, 0.55, and 0.90 days per decade, respectively, with the most rapid increases in compound and daytime heatwaves over the Qinling Mountains. Composite analyses and attribution based on redundancy analysis and hierarchical partitioning revealed distinct land-atmosphere pathways. Daytime heatwaves were primarily associated with atmospheric dryness, with vapor pressure deficit contributing 24%. Nighttime heatwaves were dominated by downward longwave radiation, which contributed 35%. Compound heatwaves reflected coupled day-night feedbacks, with nocturnal radiative insulation and daytime atmospheric dryness contributing 16% and 6%, respectively. These findings provide a systematic regional assessment of the differentiated formation pathways of daytime, nighttime, and compound heatwaves in the Loess Plateau-Qinling hydroclimatic transition zone, and support improved heatwave monitoring and adaptation in transitional climates.