order to investigate the effect of different growth stages on the nutritional quality of feed oats, three oat varieties (Zhangyan No. 4, Mengyan No. 1 and Quebec) were selected, and three growth stages of 90, 82 and 74 days were set up, respectively. The agronomic traits, nutritional quality and yield indexes of oats were measured at the filling stage. The results showed that the plant height and tillering number per plant of Zhangyan No. 4 at 74 days were significantly higher than those at 82 days and 90 days ( P<0.05), the spike length and spikelet number at 74 days were significantly higher than those at 90 days (P<0.05). The plant height, tillering number per plant, spike length and spikelet number of Mengyan No. 1 at 82 days were significantly higher than those at 74 days and 90 days (P<0.05). The plant height, tillering number per plant, spike length and spikelet number of Quebec at 90 days were significantly higher than those at 74 days and 82 days (P<0.05). The content of crude protein (CP), crude ash (Ash) and crude fat (EE) of Zhangyan No. 4 decreased with the increase of the growing stage, the content of neutral detergent fiber (NDF) and acid detergent fiber (ADF) increased with the increase of growing stage. When the growth stage was 74 days, the relative feeding value (RFV), the amount of fresh grass and hay were the highest, and the fresh-dry ratio was the lowest. The content of CP, Ash and EE of Mengyan No. 1 increased first and then decreased with the growth stage. The content of NDF and ADF of Mengyan No. 1 was the lowest at 82 days growth stage, and the RFV, fresh grass yield and hay yield were the highest at 82 days, and the fresh-dry ratio was the lowest at 82 days. The content of CP, Ash and EE in Quebec oat grass increased with the increase of the growing stage, while the content of NDF and ADF decreased with the increase of the growing period. When the growth stage was 90 days, the RFV, fresh grass yield and hay yield in Quebec were the highest, and the fresh-dry ratio was the lowest. Among the three varieties, the RFV, the fresh grass weight and hay weight of Zhangyan No. 4 were significantly higher than those of Mengyan No. 1 and Quebec (P<0.05), and NDF was significantly lower than those of Mengyan No. 1 and Quebec (P<0.05), and the ADF was significantly lower than those of Mengyan No. 1 (P<0.05). The study indicates that Zhangyan No. 4 has a better growth period at 74 days, Mengyan No. 1 has a better growth period at 82 days, and Quebec has a better growth period at 90 days. Zhangyan No. 4 has the best nutritional quality, which is suitable for planting in Inner Mongolia. [ABSTRACT FROM AUTHOR]