A rapid method was developed for the determination of 5 common fatty acids, palmitic acid, stearic acid, oleic acid, linoleic acid and linolenic acid in industrial oleic acid based on ultra_performance convergence chromatography_mass spectrometry ( UPC_MS) . The sample was dissolved by n_hexane, followed by clean_up of extract using 0. 22 μm organic phase filter. The fatty acids were separated in 3 min on the column of Acquity UPC2 BEH 2_EP by gradient elution with carbon dioxide and methanol/acetonitrile (1∶1, V/V) system, and finally detected by MS detector in ESI- mode. Through the optimization of UPC2_MS condition, the reasonable linearity was achieved for all the analytes over the range of 0. 5-100 mg/L with the correlation coefficients ( R2 ) greater than 0. 9985. The recoveries for five fatty acids at three spiked levels were in the range from 89 . 3% to 106 . 67% with relative standard deviations of 0 . 8%-3 . 0%. The limits of detection for target compounds in the method ranged from 0. 07 mg/L to 0. 26 mg/L. The real sample analysis showed that this method was simple,fast and had a good separation effect. There was no need of derivatization for fatty acid samples. This work would provide a fast and effective detection method for UPC2 technology in oil related research field.