Abstract: This study developed a method for the simultaneous determination of four Alternaria mycotoxins in maize by ultra-high performance liquid chromatography-tandem mass spectrometry. Samples were purified by solid-phase extraction column after pulverization and extraction by methanol-acetonitrile-sodium dihydrogen phosphate buffer, then separated on an XBridge BEH C₁₈ with gradient elution by methanol and 1.0 mmol/L ammonium bicarbonate aqueous solution, and detected by UPLC-MS/MS under negation (ESI^-) electrospray ionization and MRM models. The matrix-matched external standard calibration was used for quantitation. Tenuazonic acid (TeA), alternariol (AOH), and tentoxin (TEN) showed good linearity (r> 0.999) in the concentration range of 0.1-100.0 μg/L, as well as alternariol methyl ether (AME) in the concentration range of 0.1-10.0 μg/L. The detection limit for 4 Alternaria mycotoxins was 0.005-1.002 μg/kg. The average recoveries of TeA, AOH, and TEN were 78.4%-100.3% and the relative standard deviation was 2.2%-8.9% when TeA, AOH, and TEN were 4.0-100.0 μg/L, and AME was 0.4-10.0 g/L, indicating that this method had high precision and accuracy and could meet the detection requirements of the 4 kinds of Alternaria mycotoxins in maize.