A method was developed to analyze the distribution of thioether compounds in model sulfur compounds by oxidation and ICP-AES analysis and then applied to analyze hydrotreated base oil. Model thioethers were oxidized to the corresponding sulfoxides by tetrabutylammonium periodate and sodium metaperiodate, and the reduced periodate was quantitatively precipitated in the form of silver iodate. The silver iodate was transformed to AgNO3 after calcination and the addition of concentrated nitric acid. The concentration of Ag+ was determined by ICP-AES, and the concentration of thioethers was calculated with a relational equation. Aliphatic thioethers could be oxidized to sulfoxides under reflux by tetrabutylammonium periodate, and all thioethers could be oxidized to sulfoxides under reflux by sodium metaperiodate, and then the contents of aliphatic thioethers and total thioethers were determined in sample oil. The thioethers in Kelamayi hydrotreated transformer base oil were analyzed by the same method. Research indicated that this method has a high sensitivity and good selectivity.