Objective To establish an analytical method for simultaneous determination of 55 illegal addition of compounds in doet foods by ultra-performance liquid chromatography tandem mass spectrometry.Methods After ultrasonic extraction with methanol， the samples were separated on Agilent Eclipse Plus C₁₈ RRHD column （2.1 mm×100 mm， 1.8 μm） with gradient elution using a mobile phase of 0.1% formic acid aqueous solution and acetonitrile. Under positive and negative ion scanning conditions， dynamic multiple-reaction monitoring mode was used for monitoring.Results The 55 illegal addition of compounds showed good linear relationship in the corresponding linear range with all the correlation coefficient greater than 0.995. The average recoveries were 75%-125%， and the relative standard deviations were less than 12%， the LODs were all in the range of 0.02-1.25 μg/g. Fifty batches of samples were tested by this method. Fluoxetine， sibutramine， N-monodesmethyl sibutramine， N-didesmethyl sibutramine， bisacodyl， torasemide were detected in 38 samples.Conclusion This method is simple， rapid， sensitive， efficient and accurate， which can be widely applied in the high-throughput detection of illegally added chemicals in different kinds of diet foods matrices.