Using KN4010 as a base stock, we monitored changes in peroxide value and oxygen-containing compounds were monitored against time at high temperature, using iodometry and infrared spectroscopy (IR), in order to investigate the mechanism of oxidation of a hydrotreated lube base oil. The results of the tests indicate that the thermal oxidative mechanism conforms to the radical reaction theory, which is in the medium oxidative stage. The indirect analytical method of infrared spectroscopy is an effective method to study oxidative mechanisms. The content of carbonyl compounds and hydroxyl compounds decreased, and the content of hydroxyl compounds showed a slight increase at high temperature. No organic acids or esters were generated during the oxidative process.