Abstract: Sweet sorghum is a high-energy crop which has many applications, such as producing sugars and fuel ethanol. The sweet sorghum stalk residues are discarded as waste. However, there are fat, protein, crude fiber and other carbohydrates in stalk residues which can be used to make protein feedstuff. To achieve the rapid promotion and large-scale application of producing protein feedstuff using sweet sorghum stalk residues, the solid state fermentation system was used. First, the physical and chemical parameters of the sweet sorghum stalk residues were determined, the total content of cellulose, hemicellulose and lignin was 73.75% (dry weight, the same below) and the crude protein content was 2.27%. Secondly, the combination of Aspergillus nige, Trichoderma reesei, Candida utilis and Lactobacillus casei was optimized. The optimal combination of the strains was selected based on the component change of crude protein, cellulose, hemicellulose, lignin, crude ash and crude fat. The results showed that the fermentation after adding 4 strains was proper. In this condition, the cellulose content decreased by 27.0%, and the hemicellulose content decreased by 15.72%. The crude protein content in the combination added with Lactobacillus casei increased by 26.96%, the crude ash content decreased by 15.49% and the crude fat decreased by 18.15%, compared with those without adding Lactobacillus casei. Third, based on the optimal combination of the strains, 1% and 3% urea were respectively added in the sweet sorghum stalk residues to confirm the optimal content of urea. It indicated that the contents of crude protein and true protein were significantly improved with the addition of 1% urea. The true protein content was increased by 21.90% compared with that without the addition of urea under the same condition. In conclusion, the crude protein content of sweet sorghum stalk residues increased from 2.27% to 7.14% and its true protein increased from 2.01% to 6.41% after 8 days under the raw solid state fermentation along with inoculating 4 strains and adding 1% urea. This study provides an effective process to produce protein feedstuff from the raw sweet sorghum stalk residues feasibly on a large scale. It is helpful to explore an alternative of protein feedstuff in the animal husbandry industry. On the other hand, this can alleviate the environmental pollution caused by the accumulation of the sweet sorghum stalk residues, and has a very promising future.