By using the high performance liquid chromatography(HPLC), this paper detected the degradation dynamics and final residue of 0.5% emamectin benzoate microemulsion and found the degradation of 0.5% emamectin benzoate microemulsion tobacco conformed to the first class kinetics equation of the chemical reaction, its degradation curve equation was C= 0.255 8e-0.325 3t, and the degradation half-life times were 2.13 days, linear correlation coefficient(R2) was 0.884 3. The final residue test showed that residues of emamectin benzoate was very low in tobacco samples 20 days later after its being sprayed, lower than 0.006 mg/kg. there was no emamectin benzoate detected in tobacco 30 days after its being sprayed.