Abstract: An effective etching technique is desirable for processing the rough CVD diamond thick films. In the paper, CVD diamond thick films were etched by rare-earth compound ink self-prepared. The etching process was taken in the atmosphere at 600 ℃, a temperature below the oxidation temperature of diamond. A kind of inexpensive and safe rare-earth compound ink mainly made of Ce and La salts was used in this technique for the etching of CVD diamond film. The morphology of the samples was studied by SEM.The experimental results show that the process is simple and efficient for polishing the CVD diamond thick films rapidly.