Abstract: A rapid screening method for 173 pesticides in onion was established using liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF/MS). Onion samples were extracted with 1% acetic acid in acetonitrile, salted out, shaken and centrifuged, then cleaned-up by SPE column with Carb/NH₂. The LC-QTOF/MS detection was operated in the positive ion all ions MS/MS scanning mode of electrospray ionization. The important parameters such as maximum number of characteristic ions, co-elution score and peak height threshold were optimized for the qualitative screening, and the final screening parameters were determined for analysis of the collected results. Meanwhile, the methodological parameters of 173 pesticides in onion were investigated. The results showed that the SDL and LOQ of 167 pesticides were 0.001-0.005 mg/kg and 0.001-0.01 mg/kg, respectively, and it was 0.01-0.025 mg/kg and 0.02-0.05 mg/kg for the remaining 6 pesticides. These pesticides had good linear relationship in the test concentration range. The results of the recovery experiments showed that the average recoveries (n=5) of 153, 168 and 165 pesticides at three different levels (1 × LOQ, 2 × LOQ, 10 × LOQ) were in the range of 70%-120%, respectively, and the RSDs were all within 20%. The established screening method was applied to the proficiency test of pesticide residues in fruits and vegetables organized by the European Union in 2020 (EUPT-FV22). The pesticides spiked in onion were accurately screened, and the quantitative results were satisfactory. The results show that the LC-QTOF/MS screening method established in this work is accurate and reliable, and is suitable for rapid screening and accurate quantification of multi-pesticide residues in onion.