In order to examine the effect of emamectin benzoate to Frankliniella occidentalis, the toxicity of this insecticide to the adult and 2nd instar of F. occidentalis were studied by dip method in this paper. In addition, the content of soluble protein, soluble sugar and lipid in F. occidentalis were also tested after these insects were exposed to medial lethal doses of emamectin benzoate for the following exposure times: 2, 4, 6, and 8 h. Furthermore the utilization rate of the energy source in F. occidentalis was calculated after the insects were exposed to emamectin benzoate until dead at the medial lethal doses. The results showed that emamectin benzoate had different toxicity to the adult and 2nd instar of F. occidentalis, and the medial lethal doses were 1.11 and 0.62 mg/L, respectively. With the extension of exposure time at medial lethal doses of emamectin benzoate, there was significant a increase or decrease on the content of soluble protein, soluble sugar and lipid in F. occidentalis adult, but no significant variation on their content in F. occidentalis nymph. When the F. occidentalis was dead under the medial lethal doses exposure, there was significant difference in the utilization rate of the three kinds of energy sources in F. occidentalis, the utilization was soluble sugar（74.12%）> soluble protein（58.10%）> lipid（42.13%）in adult, significantly higher than that in nymph at any kind of the three energy sources, and the utilization was soluble sugar（64.01%）> soluble protein（48.12%）> lipid（36.48%）in nymph. According to the results, we could conclude that the different variation and utilization of energy source between F. occidentalis adult and nymph under the exposure of emamectin benzoate, may have some relationship to their different tolerance to this insecticide.