Abstract: The Qinling-Daba Mountains have been the most important geo-ecological transition zone in China, with a high degree of environmental complexity, biodiversity, and climate sensitivity. Based on the field survey quadrat data and the collected data of typical mountain altitudinal belts in the Qinling-Daba Mountains, the multi-dimensional variation and differentiation of typical mountain altitudinal belts were compared from the perspective of belt width. The results showed that: (1) From north to south, the width of the deciduous broadleaved forest belt gradually decreased from 2 200 m to 100 m, and disappeared in the Tangjiahe area. The evergreen and deciduous broad-leaved mixed forest belt and the coniferous and broad-leaved mixed forest belt showed a nearly linear increase trend. The coniferous forest belt width increased from 300 m to 550~900 m. (2) From west to east, along the slope of the mountains, the width of the evergreen broad-leaved forest belt increased from 400 m to 600 m. The width of the evergreen and deciduous broad-leaved mixed forest belt increased from 500 m to 800 m. The eastern coniferous and broad-leaved mixed forest belt was about 100m wider than the western one. The deciduous broad-leaved forest belt was wider in the middle of the Qinling-Daba Mountains and narrower in the east and west, while the coniferous forest belt was the opposite. (3) The aspect differentiation effect of Daba Mountains on the belt width was more obvious than that of Qinling Mountains. In terms of individual mountains, the belt width of evergreen deciduous broad-leaved mixed forest and coniferous forest on the southern slope was usually wider than that on the northern slope, while the deciduous broad-leaved forest belt was narrower on the southern slope. The coniferous and broad-leaved mixed forest belt had a wider width on the southern slope of Qinling Mountains and the northern slope of Daba Mountains than on the other side with a difference of 200~300 m. (4) The width of typical altitudinal belts was the result of the combined action of many factors. Regional climate determined the nature of the baseband and the basic sequence of the altitudinal belt spectrum. The mountain base elevation had an upward extrusion effect on the belt width, and the relative height of the mountain determined the potential spatial distribution range of the altitudinal belt spectrum. The multi-dimensional differentiation of the width of typical altitudinal belts in Qinling-Daba Mts. reflected the transition and complexity of China's north-south transitional zone, which can provide a scientific basis for the vertical protection of vegetation in nature reserves.