Abstract: The high crystallinity and low soluble dietary fiber (SDF) content of okara dietary fiber (ODF) restrict its functional application performance. In this study, a synergistic solid-state modification strategy was constructed and evaluated: alkali-assisted dry ball milling (A-BM) was adopted for structural preactivation, followed by acetylation or carboxymethylation chemical substitution to improve the reaction reactivity, physicochemical properties, and adsorption functions of ODF.A total of Test samples were prepared, including raw ODF, ball-milled ODF (BM), A-BM-pretreated ODF (A-BM), and their acetylated and carboxymethylated derivatives (ODF-A, BM-A, A-BM-A, ODF-C, BM-C, and A-BM-C). Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and particle size distribution analysis were conducted for structural characterization. A-BM pretreatment severely destroyed the crystalline structure of ODF, decreased particle size, and exposed more hydroxyl groups, thereby prominently increasing the SDF content (raw ODF: 3.07%; BM: 14.20%; A-BM: 38.02%). Mechanical activation remarkably promoted the reaction efficiency of subsequent chemical substitution. The degree of acetylation rose from 0.022 for acetylated or carboxymethylated derivatives (ODF-A) to 0.035 for BM-A and 0.052 for A-BM-A. Meanwhile, the degree of carboxymethyl substitution increased from 0.257 for ODF-C to 0.483 for BM-C and 0.721 for A-BM-C. Morphological characterization showed that modified dietary fibers formed loose and porous network structures, accompanied by enhanced water solubility and hydration capacity. All modified samples showed obvious particle size reduction, among which A-BM-C possessed the minimum particle size (D_3,2 approximately 8.82μm). Functional verification confirmed the prominent optimization of adsorption capacities. At pH 7.0, the cholesterol adsorption capacity (CAC) was elevated from 7.04 mg/g for native ODF to 26.38 mg/g for A-BM-C. A-BM-C also achieved the maximum glucose adsorption capacity (GAC) and glucose dialysis retardation index (GDRI), with a GAC of approximately 2.94 mmol/g and a 30 min GDRI of approximately 58.19%. In summary, the combined treatment of alkaline activation and dry ball milling coupled with chemical substitution efficiently boosted the structural reactivity and functional properties of ODF under mild reaction conditions. Carboxymethylation modification after alkaline ball milling exerted the most pronounced enhancement on SDF yield, substitution degree, hydrophilicity, and adsorption capacities for cholesterol and glucose. By contrast, acetylation modification mainly enhanced the oil-binding capacity of ODF. This synergistic modification method can serve as an efficient technical route for the high-value comprehensive utilization of ODF.