Acorn starch is a high-quality non-grain starch with high gel strength and high resistant starch content, while its poor swelling performance, high retrogradation tendency and insufficient processing stability restrict its large-scale application in the food industry. In this study, acorn starch was modified by ball milling at different rotational speeds for 30 min to explore the regulation mechanism of mechanical modification on its structure and functional properties and achieve its targeted application. The changes in molecular structure, crystal structure, particle morphology, physicochemical, pasting and thermodynamic properties of modified acorn starch were systematically investigated. The results indicated that ball milling did not change the molecular skeleton of acorn starch, but effectively destroyed its crystal structure and double-helix orderliness, with starch crystallinity gradually decreasing with the increase of rotational speed. Starch particle size presented a nonlinear trend of initial reduction and subsequent recovery, and the maximum specific surface area of 942.70 m²·kg?¹ was obtained at 300 r·min?¹. Increased ball milling intensity significantly improved the hydrophilicity, solubility and water holding capacity of acorn starch. Moderate ball milling (300–450 r·min?¹) optimized starch gel structure, reduced water separation and enhanced freeze-thaw stability. Nevertheless, excessive milling (≥750 r·min?¹) caused structural collapse of starch, resulting in a sharp drop of RVA peak viscosity from 5334.67 cP to 267.67 cP, along with decreased gelatinization enthalpy and deteriorated thermal stability. This study confirmed the nonlinear rule that moderate ball milling improves starch quality while excessive milling leads to performance degradation. Starch modified at medium and low speeds exhibited excellent freeze-thaw stability, whereas high-speed modified starch possessed high solubility, low viscosity and non-high-temperature gelatinization performance, realizing differentiated industrial applications. This work provides theoretical and technical support for the targeted preparation of functional acorn starch ingredients and the high-efficiency utilization of acorn starch resources.