Bacil us thuringiensis strain Bt20 isolated in our laboratory with independent intel ectual property right, had a high insecticidal activity that lepidopteran larvae and possess better popularization and application value. In this paper, we studied that how to optimize the carbon source and nitrogen source materials of Bt20 strain liquid fermentation medium, with the strain Bt20 fermentation broth absorbance value and the virulence against the 2nd instar larvae of Plutel a xylostel a as indices. Firstly, the single factor tests was performed to optimize the carbon source and nitrogen source materials of strain Bt20 liquid fermentation medium, the obtained optimal carbon source material and nitrogen source materials were the corn flour and the maggot, yeast flour, fish meal, soybean flour, respectively. Secondly, the orthogonal test was performed to the optimal carbon and nitrogen source materials. Experimental results showed that the appropriate formula of liquid fermentation medium was 3.0% corn flour, 3.0% maggot, 3.0% soybean flour and 2.0%yeast flour. Absorbance value of the optimal fermentation medium was 1.4733 and corrected mortality was 98.31%against the 2nd instar larvae of Plutel a xylostel a, after 3 d. The optimal fermentation medium was significantly better than the fish meal fermentation broth which the absorbance value was 1.0683 and corrected mortality was 88.14%. The optimized formula can improve the yield and virulence of fermentation products, reduce production costs, and provide fundamental basis for the commercialization and large-scale application of Bt20.%苏云金芽胞杆菌（Bacillus thuringiensis）Bt20菌株为东北农业大学农业昆虫与害虫防治实验室分离出来的具有独立知识产权的菌株，其对鳞翅目幼虫具有较强杀虫活性，具有良好推广应用价值。文章进行优化Bt20菌株的液态发酵培养基碳源、氮源材料研究，试验以Bt20菌株发酵液吸光度值及对2龄小菜蛾的毒力效果为指标，首先采用单因素试验对Bt20菌株发酵培养基的碳源及氮源进行优化，筛选得到最佳碳源为玉米粉，最佳氮源为蝇蛆、酵母粉、鱼粉、大豆粉；运用正交试验设计方法对优化后的碳、氮源进行正交试验，明确Bt20菌株最佳液态发酵培养基配方为：玉米粉3.0%、蝇蛆3.0%、大豆粉3.0%、酵母粉2.0%；最佳发酵培养基下，Bt20发酵液吸光度值为1.4733，发酵液处理2龄小菜蛾，3 d后校正死亡率为98.31%，显著优于鱼粉发酵液的吸光度值1.0683及校正死亡率88.14%，提高发酵产物产量和毒力，降低生产成本，可为Bt20商品化及大规模应用提供基础依据。
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