Abstract: The polishing technology of diamond films has become one of the key technologies for the popularization and application of diamond films. In recent years, a number of alternative polishing techniques of diamond films have been reported, and each having technological advantages and disadvantages. The thermochemical polishing technology based on the diffusion of carbon atoms has good prospect due to its superior properties, e.g. excellent polishing quality, high efficiency and very small mechanical damage. But up to now, the thermochemiacal polishing method, in which the polishing plate is heated to high temperature, either need complicated apparatus or the polishing process is very costly. In this paper, the development and characteristics of thermochemical polishing techniques were reviewed, and the effects of different factors on thermochemical polishing of diamond films were also reviewed. Finally, a new super-high speed polishing method of diamond films has been proposed, which was aided by the rare earth metal. The effects of polishing temperature on the theoretical removal rate of diamond films has been analyzed by using diffusion mechanics, and the results agree well with the experiment data. The super-high speed polishing method has the advantages of simple apparatus and precision polishing for diamond films, etc.