Abstract: The fermentation quality of sorghum-sudangrass hybrids (Sorghum bicolor×Sorghum sudanense) is poor because of their high moisture contents. In this study, we analyzed the effects of different storage modes on the fermentation quality of a sorghum-sudangrass hybrid. A sorghum-sudangrass hybrid was mixed different types of hay (corn stalk, wheat straw, and alfalfa hay) at different proportions (12.5, 25.0, 37.5 and 50.0 kg/t). Then, the nutritive value, fermentation quality, 72 h dry matter digestibility, and gas dynamics were measured using an in vitro system that simulated rumen fermentation. The results showed that the silage produced from the sorghum-sudangrass hybrid had a high butyric acid content, and a poor Flieg evaluation ranking. The addition of all types of hay significantly improved the fermentation quality of stored silage. The addition of wheat straw resulted in the best fermentation quality, while the addition of alfalfa hay resulted in the best nutritive value. The addition of alfalfa hay resulted in the highest values for IVDMD (in vitro dry matter digestibility), c (gas production speed), and AGPR (speed when gas production was one-half of the maximum). There was no significant difference in GP_72h (accumulated gas production in 72 h), A (ideal maximum gas production), and lag (lag time of gas production) among silages produced with the three types of hay. In terms of the amount of hay added, the addition of 25.0 kg/t resulted in the best fermentation quality and the highest half-time content, and the addition of 50.0 kg/t resulted in the best nutritive value and the highest IVDMD. The addition of 37.5 kg/t hay resulted in the highest c and AGPR values. The amount of hay added did not significantly affect GP_72h, A, or lag. Considering the nutritive value and fermentation quality, the best mixed silage was produced by adding 37.5 kg/t wheat straw. The addition of 50.0 kg/t alfalfa hay gave the highest IVDMD content, the addition of 37.5 kg/t alfalfa hay gave the highest gas production rate, and the addition of 50.0 kg/t wheat straw resulted in the highest GP_72h and A.