Diamond has many outstanding physical, chemical, optical, mechanical, and electrical properties such as the highest thermal conductivity, the extreme chemical inertness, the highest known hardness, the lowest compressibility of known material, high in Young’s modulus, low in friction coefficient, wide in band gap, and a wide optical transparency bandwidth. Thus, diamond can be a potential solution to many advanced engineering problems. Though diamond possesses all those excellent properties, high cost and difficulty in machining have hindered its industrial applications. Nowadays, using CVD method to synthesize high quality diamond film is a rather mature and stable technology. Diamond grains normally get bigger and the surface gets rougher when the film gets thicker as the result of competition growth. Depending on the film thickness and growing conditions, the surface roughness can vary from tens micrometer to a few micrometers. However, a smooth surface in many industrial applications is a necessity. Many researches have been conducted to improve the surface roughness of CVD diamond film by various approaches such as by mechanical polishing, chemical polishing, thermo-chemical polishing, chemical- assisted mechanical polishing, laser ablation, ion beam irradiation, ECR plasma polishing, and reactive ion etching. Unfortunately, none of them could quickly and efficiently lower the surface roughness, especially in terms of large area and thick CVD diamond film. In this thesis, the CVD diamond film was conducted with the thermo-chemical polishing, laser ablation, inducted coupling plasma, and reactive ion etching, respectively. The research aimed to improve the surface roughness and to investigate the mechanism of material removal. The SEM micrographs and micro-Raman were used to analyze the morphology and microstructure of the obtained surface. The results showed that the compound polish method could effectively shorten the processing time needed to polish the CVD diamond by weakening its surface structure.