Abstract: Protein content in feed is a key index for evaluating feed quality, However, recent reports of determine the protein content of feed on dietary for feeds tuffs investigated as potential sources of protein content (yeast, lactic acid bacteria, etc.) and protein content of the forage. The protein content of feed yeast strains directly determines the protein content of feed, so it becomes the key to obtain good feed yeast strains. In this study, a heavy ion ¹²C⁶⁺ beam with an energy of 80 MeV/u was used for irradiation mutagenesis and breeding of starter yeast NJ3236(protein content of 40.64%), and the strains were screened and rescreened to obtain 100G-2 strain with high protein content. The protein content of the 100G-2 strain increased by 10.08% compared with that of the strain NJ3236. Then response surface analysis was used to optimize the fermentation medium. The optimal ratio of medium showed that sweet sorghum juice 20.95 g/L, corn steep liquor 18.17 g/L and magnesium sulfate 1.60 g/L. Under this condition, the soluble protein concentration reached 1.381 mg/mL, which was 8.7% higher than that before optimization.