Abstract: To clarify the regulatory effects of plant growth regulators on seed yield and related traits of Eragrostis nigra, chlormequat chloride, trinexapac-ethyl, and their mixture were sprayed at the tillering and jointing stages. The effects of different growth regulator treatments on agronomic traits, seed quality, seed yield, and yield components of Eragrostis nigra were investigated. The results showed that both chlormequat chloride and trinexapac-ethyl significantly reduced plant height, increased stem diameter, and enhanced tiller number, fertile shoot number, and spikelet number, but had no significant effects on seed number, floret number, or thousand-seed weight. Chlormequat chloride significantly increased germination rate but had no significant effect on seed setting rate, whereas trinexapac-ethyl showed the opposite effect. Both chlormequat chloride and trinexapac-ethyl effectively increased the theoretical and actual seed yields of Eragrostis nigra. Comprehensive analysis using the membership function method indicated that the mixed application was more effective than either compound applied alone, with the C₃T₂ treatment showing the most pronounced promoting effect.