Abstract: A method for determination of cyflumetofen and its metabolite o-trifluoromethyl benzoic acid in plant origin food (such as fruit, vegetable, tea) by UHPLC-MS/MS was established. 4 g of sample (1 g of tea sample) was extracted by oscillation in a mixture of 10 mL of 90% (φ) acetonitrile solution, 1.0 mL of 1 mol·L^-1 hydrochloric acid solution, 3 g of anhydrous sodium sulfate and 2 g of sodium chloride for 2 min. After centrifuging, the upper acetonitrile phase was injected into graphitized carbon black solid phase extraction small column for purification, and 6 mL of a mixture of acetone and methanol at volume ratio of 2:3 was used for elution. The effluent and eluent were collected and blown to nearly dry by nitrogen, and 2 mL of 40% (φ) acetonitrile solution was added. After filtering, the filtrate was introduced into UHPLC-MS/MS for determination. Waters ACQUITY UPLC BEH C₁₈ column was used as stationary phase, and a mixture of acetonitrile and 5 mmol·L^-1 ammonium acetate solution containing 0.2% (φ) formic acid with different volume ratios was used as the mobile phase for gradient elution. ESI⁺, ESI^- and MRM mode were adopted in MS/MS analysis. The working curves were drawn with the matrix matching of mixed standard solution series. It was showed that linear relationships between mass concentrations of cyflumetofen and o-trifluoromethyl benzoic acid and their peak areas were kept in the range of 10-500 μg·L^-1 for sample of soybean, eggplant, cabbage, tomato, apple and green tea, with detection limits (3S/N) in the range of 0.1-2.9 μg·kg^-1. Recovery test was made on above negative samples by standard addition method, giving results of cyflumetofen and o-trifluoromethyl benzoic acid in the range of 78.2%-93.0%. RSDs (n=10) of the determined values were ranged from 2.8% to 14%, and RSDs of reproducibility (n=5) were less than 15%.