Scientific understanding of the evolution law of territorial space patterns and the ability to reveal the formation mechanism hold great significance for the sustainable utilization of territorial resources and the high-quality green development of the Yangtze River Economic Belt (YREB). In this study, we used the spatial chord diagram, landscape pattern index, and geographical probe to explore the evolution characteristics and formation mechanism of the territorial space pattern of the YREB from 2000 to 2020. The results showed the following: (1) The territorial space showed obvious geographical hierarchical distribution characteristics in the topographic gradient. Production and living space was dominant throughout the low and middle terrain region. Ecological space was dominant throughout the high-terrain regions. With the increase of altitude and slope, production and living space contracted, whereas ecological space areas expanded. (2) Since 2000, the territorial space has changed more dramatically. Over time, living space tended to increase, and production and ecological space tended to decrease, but ecological space was always dominant. In space, the geographical differentiation of territorial space was more obvious, and the pattern was relatively stable, with production space distributed primarily in the middle and lower reaches, living space distributed primarily in the lower reaches, and ecological space distributed primarily in the middle and upper reaches. The inter-transformation between territorial spaces was more frequent, and the transformation trajectory was diversified. (3) The fragmentation, heterogeneity, and dispersion of territorial space landscape patches throughout the whole region increased, and the balance and diversity of territorial space utilization improved. (4) Natural factors have continued to weaken the intensity of their effect on territorial space. Human factors gradually increased the extent of their interference in the territorial space. There are significant differences in the extent of the role of these different factors on the territorial space of the whole region and each basin. Natural and human factors jointly promoted the formation and development of the territorial space pattern.