Abstract: The Castanea henryi sample (5.00 g) was taken and placed into a 50 mL-plastic centrifuge tube, followed by the addition of 15 mL of water. The mixture was shaken well and settled for 30 min. A ceramic homogenizer was added to the centrifuge tube, followed by 15 mL of a mixed solution of acetic acid and acetonitrile at volume ratio of 1∶99. The tube was placed in an ice-water bath, and then 6.0 g of magnesium sulfate anhydrous and 2.0 g of sodium acetate anhydrous were added. After the rapid and intense shaking, the mixture was settled for 10 min in the ice-water bath and then centrifuged for 5 min. 8 mL of the supernatant was placed to a 15 mL-centrifuge tube containing 1 000 mg of magnesium sulfate anhydrous +300 mg of C₁₈+300 mg of N-propylethylenediamine (PSA). The mixture was vortexed for 5 min and centrifuged for 5 min. An aliquot (2 mL) of the supernatant was taken and blown to near dryness by nitrogen at 35 ℃ in water bath. After ethyl acetate was added to 1 mL, the mixture was vortexed and homogenized, and passed through a 0.22 µm organic filter membrane. The residues of 20 pesticides in the filtrate were determined by gas chromatography-triple quadrupole tandem mass spectrometry. The 20 pesticides were separated on HP-5MS UI column by programmed temperature, ionized by EI ion source, detected by multiple reaction monitoring (MRM) mode, and quantified by external standard method with matrix matching mixed standard solution series for drawing working curves. It was shown that linear relationships between the mass concentrations and the corresponding quantitiative ion pairs peak areas of 20 pesticides were kept in the range of 5—500 μg·L⁻¹, and detection limits (3S/N) ranged from 0.051 μg·kg⁻¹ to 1.4 μg·kg⁻¹. Test for recovery was made according to standard addition method, giving recoveries in the range of 79.2%—97.1%, and RSDs (n=6) of the determined values were less than 8.0%.