In this article, taking use of KN4010 as base stock, iodometry and infrared spectroscopy were carried out to monitor its change of peroxide value and oxygen-containing compounds against time under ultraviolet radiation, and oxidative mechanism of hydrotreated lube base oil was investigated in detail. The results of this test indicate that its light oxidative mechanism conforms to the radical reaction theory that is in the medium oxidative stage. Test of peroxide value confirms that the oil sample is very sensitive to ultraviolet radiation. The contents of carbonyl compounds and hydroxyl compounds show a decreased trend and the content of hydroxyl compounds are almost unchangeable under ultraviolet radiation. No organic acid and ester is found under the oxidative process.