In this study, an improved tribology test rig has been applied to conduct the study on transformation mechanism between the frictional interface under the lubrication of DOS with steel/steel contacts. The results indicated that the nature of wear debris was nano-sized Fe3O4 particles coated by a great deal of carbonaceous matter, which could act as a solid lubricant on the friction interface. The wear debris filled the grooves in steel surfaces and a bright black tribofilm was generated during test. The analysis results of GC-MS showed that C-C chemical bonds of DOS molecules at the tertiary carbon were easier to break during the tribochemical reaction process, and the possible tribochemical reaction mechanism of DOS molecules in this experiment was proposed.