In this article, a kind of method was described for separation and characterization of the trace organic phosphorus compounds in hydrotreated lube base oil. First, the base oil was extracted with methanol containing 2% hydrochloric acid, and then the extracted portion was adsorbed on neutral aluminum oxide and eluted with petroleum ether, benzene, chloroform, and 9:1 tetrahydrofuran-ethanol in sequence; finally the fraction acquired was characterized by gas chromatography-mass spectrometry, respectively. The result of the test indicates that only one kind of organic phosphorus was found in hydrotreated lube base oil, gas chromatography-mass spectrometry and gas chromatography-Fourier transform infrared spectroscopy (GC-FTIR) were used to characterize the organic phosphorus compound, and its molecular structure is tributyl phosphate.