The evolution of sleeve structure is a core interdisciplinary issue in apparel design. From the theoretical lens of “cross-scale coupling,” this study systematically explores the intrinsic mechanisms underlying the transition from conventional to irregular sleeves and the corresponding paradigm shifts in design. Through literature review, geometric-parameter measurement, multi-scale modeling, and case analysis, we uncover the coupled relationships among key parameters—sleeve length, sleeve-cap height, and sleeve width—across micro-level fiber architectures, meso-level pattern constructions, and macro-level wearing behaviors. Results indicate that every 1 cm increase in sleeve-cap height increases overall looseness by approximately 5%; changing the cuff shape from round to square enhances functionality by 10%; irregular sleeves improve mobility by 15 % over conventional sleeves, and 80 % of participants prefer their visual impact. Based on these findings, we construct a tripartite paradigm-shift framework of “structure–function–aesthetics” and propose a new design paradigm that evolves from single-scale optimization to multi-scale synergy. The findings provide systematic theoretical support for sleeve-structure innovation and methodological reference for cross-scale apparel-structure design.