China is now the largest and only producer of avermectin in the world. However, its current yield is still lower than other similar antibiotics. Therefore, we studied the effect of nitrogen on the growth and the synthesis ability of B1a to improve the overall yield. Nitrogen had significant effects on the cell activity, PMV of Streptomyces avermitilis and the synthesis of B1a in the middle and later phase of fermentation. Additional feeding yeast powder based on carbon-dioxide evolution rate in a 100-L bioreactor significantly improved the synthesis of B1a. The production of avermectin reached 8 697 mg/L, 26.9% higher than the original process. In short, this study will serve in production enhancement of avermectin at industrial production.