This study aimed to determine the optimal harvesting time for covered barley to make grain silage, in Honam region of Korea. We harvested six varieties of barley every third day from 24 to 42 days after heading (DAH). The moisture content decreased from 62.4% at 24 DAH to 24% at 42 DAH. The moisture content at 36 DAH was 44.3%; however, moisture content at 39 and 42 DAH was lower than 40%. Yield of covered barley significantly increased from 24 to 42 DAH (p < 0.05). Yield at 36 DAH (557 kg/10a) was not significantly different from that at 39 and 42 DAH (p < 0.05). With respect to the feed value of barley grain silage, the amount of crude fiber and crude ash was different by harvesting time (p < 0.05). However, the amount of crude protein, crude fat, and total digestible nutrients (TDN) from 24 and 42 DAH was not significantly different. The pH of grain silage from 24 to 42 DAH was between 3.8 and 4.2 and it was stable until 36 DAH (p < 0.05). However, the pH of grain silage at 39 and 42 DAH was 5.2 and 5.8, respectively, which was higher than the pH of silage with good fermentation quality. The lactic acid content of barley grain silage from 24 to 42 DAH decreased from 5.5% to 0.5% (p < 0.05). The amount of lactic acid at 36 DAH was higher than that at 39 and 42 DAH (p < 0.05). With respect to moisture content, yield, feed value, and fermentation, the optimal harvesting time for grain silage of covered barley was 36 DAH. This could increase the use efficiency of harvesting machine for barley and reduce the harvesting time gap between whole barley silage and grain silage in Korea. Moreover, using barley grain silage for animal feed could reduce the import of corn.