Abstract: The relationship between concentration,droplet density, spraying volume and the efficacy of emamectin benzoate against diamondback moth were studied by the technology of bioassay in laboratory and field test. The results indicated that the LN50 (median lethal number of droplets per unit area) value dropped from 148 droplet/cm2 to 3 droplet/cm2 when the concentration of emamectin benzoate increased from 80 mg/L to 640 mg/L. The LC50 value of emamectin benzoate changed from 1.66×102 mg/L to 78.93 mg/L as the droplet density increased from 23 droplet/cm2 to 131 droplet/cm2. The maximum deposition of emamectin benzoate was observed on the front side of glass slides with 0° angle and the back side of glass slides with 90°, and the minimum was observed on the back side of glass slides with 45° angle and the front side of glass slides with 90° angle. The deposition of emamectin benzoate on cabbage leaves was affected by droplet size and concentration of emamection benzoate. At concentration of 3 mg/L, the efficacy of emamectin benzoate in fields spraying with 330 L/hm2 was lower than that of spraying with 525, 750 and 975 L/hm2. However, the efficacies in fields spraying with 525, 750 and 975 L/hm2have no significant differences. At concentration of 4.2 mg/L, the efficacies of emamectin benzoate spraying with different volume were similar. Hence, emamectin benzoate exhibited excellent controlling efficacy to diamondback moth and the spraying volume decreased significantly under condition of spraying with smaller droplet size (VMD=128.9 μm) and higher concentration (4.2 mg/L).