Based on determination for surface tension of organosilicone solution and its expansion on the solid surface,the biological activity of 5% emamectin benzoate WDG with organosilicone against beet armyworm was determined by spraying method to study their synergistic activity. The results showed that organosilicone significantly reduced surface tension of aqueous solution,and the surface tension was reduced to 26mN/m as the concentration of organosilicone was 0.01%. The organosilicone significantly raised expansion of liquid drops on solid surface,and the expansion diameter of 10 μL 0.01% organosilicone was 34 mm. The indoor toxicity results indicated that when addition dosage of organosilicone was 1%-5%,synergistic activity of 5% emamectin benzoate WDG with organosilicone against beet armyworm was significant,and increase extent of synergistic activity slowed down as organosilicone dosage was higher than 5%. Field experiment showed that the control efficacies of 5% emamectin benzoate WDG + 5% organosilicone 33 mg/L against beet armyworm were 81.57% and 82.66% after spraying for 3 and7 d respectively,which were significantly better than treatments of 5% emamectin benzoate WDG 33 mg/L,24% metaflumizone SC 96 mg/L,5% chlorantraniliprole SC 33 mg/L,20% flubendiamide WDG 40 mg/L and 15% indoxacarb EC 43 mg/L. Based on determination for surface tension of organosilicone solution and its expansion on the solid surface, the biological activity of 5% emamectin benzoate WDG with organosilicone against beet armyworm was determined by spraying method to study their synergistic activity. The results showed that organosilicone significantly reduced surface tension of aqueous solution, and the surface tension was reduced to 26 mN / m as the concentration of organosilicone was 0.01%. The organosilicone significantly raised expansion of liquid drops on solid surface, and the expansion diameter of 10 μL 0.01% organosilicone was 34 mm. The indoor toxicity results indicated that when addition dosage of organosilicone was 1% -5%, synergistic activity of 5% emamectin benzoate WDG with organosilicone against beet armyworm was significant, and increase extent of synergistic activity slowed down as organosilicone dosage was higher than 5% . Field experiment showed that the control efficacies of 5% emamectin benzoate WD G + 5% organosilicone 33 mg / L against beet armyworm were 81.57% and 82.66% after spraying for 3 and 7 d respectively, which were significantly better than treatments of 5% emamectin benzoate WDG 33 mg / L, 24% metaflumizone SC 96 mg / L, 5% chlorantraniliprole SC 33 mg / L, 20% flubendiamide WDG 40 mg / L and 15% indoxacarb EC 43 mg / L.