Abstract: The residue of acephate in tea was determined by gas chromatography. The source of uncertainty in the determination process was analyzed, each uncertainty component was evaluated, and the synthetic uncertainty and extended uncertainty were calculated. The results showed that when the residue of acephate in tea was 0.114 mg/kg, the expanded uncertainty was 0.010 mg/kg, and the concentration of sample solution and the repeatability of sample determination had the greatest influence on the results.