An analytical method was established for the determination of distearyl dimethyl ammonium chloride（DSDMAC) in dyeing and finishing textile agents by ultrasound assisted extraction combined with liquid chromatography-tandem mass spectrometry（LC-MS/MS).The sample was extracted with methanol by ultrasound-assisted extraction.The extract was filtered and then detected by LC-MS/MS with electro spray ionization source.The confirmation ion pairs were m/z 550.5/298.3，522.5/298.3，522.5/270.3，494.5/270.3,and the quantification ion pairs were m/z 550.5/298.3，522.5/298.3，494.5/270.3.The calibration curve was linear for DSDMAC in the range of 0.02-1.0 mg/L with correlation coefficient of 0.998 5.The limit of quantitation was 20 mg/kg.The recoveries of DSDMAC at the spiked range of 100-500 mg/kg were between 86% and 96%，with relative standard deviations（RSDs)of 3.2%-5.4%.The experimental results indicated that the method was rapid,sensitive and accurate,and could meet the correlative requirements for determination of DSDMAC in dyeing and finishing textile agents.