Polycrystalline CVD diamond film possesses many advanced physical and mechanical properties which makes it a very important engineering material. However, high hardness value and extreme brittleness have made CVD diamond film a very difficult material to be machined by conventional grinding and polishing processes. In the present research, diamond wafers were pretreated with RIE in an attempt to weaken the top layer and pave the way for subsequent thermochemically polishing. It was found that the diamond grains were anisotropically etched and some high aspect ratio pillar-like micro-structures were formed during the RIE process. These micropillars are relatively easy to be ruptured and removed by the subsequent polishing process. The results showed that this method could effectively speed up the polishing of CVD diamond films.