Abstract: In order to study the influence of endophytic fungal infection on the fiber and crude fat of Hordeum bogdanii during the grain setting period and to provide theoretical support for the further rational use of the grass, in the experiment, the Hordeum bogdanii infected（E+） and uninfected（E-） with Epichlo3 endophytic fungi at the grain setting period were used as research objects. They were treated with 50, 100, 150, and 200 mmol/L mixed alkali for 21 days. The difference of fiber and crude fat between E+ and E-plants under alkali stress were compared. The results showed that the content of crude fiber（CF） in stems, leaves and roots of Hordeum bogdanii increased with the increase of alkali concentration, in addition to the control group, the contents of neutral detergent fiber（NDF） and acid detergent fiber（ADF） in stems, leaves and roots of E-Hordeum bogdanii plants also showed an increasing trend. The contents of NDF, ADF, CF and acid detergent lignin（ADL） in stems, leaves and roots of E+ plants were lower than those of E-plants under alkali stress, but there was no significant difference in the content of crude fat（EE） in the stems, leaves and roots between the two plants（P＞0.05）. Endophytic fungi significantly affected the contents of NDF, ADF and ADL in stems, leaves and roots of Hordeum bogdanii（P＜0.05）. Alkali treatment significantly affected NDF, ADF and CF contents in stems, leaves and roots of Hordeum bogdanii（P＜0.05）. The interaction between alkali treatment and endophytic fungi significantly affected the NDF, ADF contents in the stems and leaves and the ADL content in the roots of Hordeum bogdanii（P＜0.05）. The results indicated that endophytic fungi could reduce the fiber content of Hordeum bogdanii under alkali stress, which was beneficial to improve the digestibility of the grass in herbivorous livestock.