In this paper, fundamental research is carried out for establishment of high-efficiency polishing technology of CVD diamond thick film, which is prepared by our lab. The main work done in this paper is as follows:1. Orthogonal polishing test was designed and the surface roughness and profile of work were measured to optimize the mechanical polishing parameters for high-efficiency polishing of the diamond film, by using of self-made mechanical polishing equipment.2. The residual stresses of the diamond film were measured by X-ray method, and the effect of the polishing condition on the stresses was investigated experimentally.3. The diamond film with crack was polished by using of a mechanical polishing machine, and the crack existed in the film was analyzed by scanning electron microscope.4. EDM method was adopted to polish the diamond film, and its removing mechanism was discussed.