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To explore the effects of absorbed dose and particle size on enzymatic hydrolysis and fermentation of reed straws (Phragmites australias), the straws were irradiated with γ-ray irradiation at different doses (0-500 kGy) and then passed through different aperture sieves after mechanical grinding. The effects of absorbed doses and sieving aperture size on particle size distribution, comminution energy, main component content, enzymatic hydrolysis conversion rate, and ethanol conversion rate of cellulose were examined, and the optimal respective sieving aperture for reed straws with different absorbed doses were determined. The results showed that with decreasing sieve aperture size, reed straw quality decreased significantly and was negatively correlated with the absorbed dose; the comminution energy of reed straws decreased with increasing absorbed doses. With respect to consistent quality of sieved reed straws, the comminution energy increased significantly with decreasing sieving particle size. In reed straws with the same absorbed dose, the enzymatic hydrolysis conversion rate and ethanol conversion rate of cellulose increased with decreasing sieving aperture size. Compared with reed straws with particle size r ˂ 0.850 mm, the cellulose enzymatic hydrolysis conversion rates in reed straws with particle size r ˂ 0.180 mm increased by 129.20%, 85.98%, and 106.63% at absorbed doses of 0 kGy, 206 kGy, and 404 kGy, respectively, and cellulose ethanol conversion increased by 136.04%, 21.75%, and 4.39%, respectively. By compre- hensively comparing the increased ratios of comminution energy, cellulose enzymatic hydrolysis conversion rate, and cellulose ethanol conversion rate, the optimal sieving aperture of non-irradiated (0 kGy) reed straws was deter-mined to be 0.850 mm, and that of reed straws irradiated with 206 kGy or 404 kGy was determined to be 0.425 mm.