The degree of forage lignification is a key factor affecting its digestibility by ruminants such as cattle and sheep. Sudan grass ( S.) is a high-quality sorghum forage, and its lignocellulose is mostly stored in the secondary cell wall. However, the secondary cell wall synthesis mechanism of Sudan grass has not yet been studied in depth. To further study the secondary cell wall synthesis mechanism of Sudan grass using established transcriptome data, this study found that , a homologous gene of , is related to the secondary cell wall synthesis of Sudan grass. Accordingly, we constructed a -overexpressing line of to investigate the function of the gene in secondary cell wall synthesis. The results showed that the overexpression of the gene could significantly increase the lignin content of . Based on subcellular localization analysis, CcNAC6 is found in the nucleus. In addition, yeast two-hybridization screening showed that CcCP1, associated with secondary cell wall synthesis, can interact with CcNAC6. Therefore, the above results indicate that has a positive regulatory effect on the secondary cell wall synthesis of Sudan grass, and it is speculated that CcNAC6 may be the main regulator of the secondary cell wall synthesis of Sudan grass through its interaction with another regulatory protein, CcCP1. This study provides a theoretical basis and new genetic resources for the creation of new Sudan grass germplasm with a low lignin content.