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The movement of the Co-rich binder phase and its interaction with growing diamond particles during deposition were investigated by repeated observations of the same site on a WC-Co substrate surface. Both etched and unetched (as-polished) specimens of WC 5Co were used for deposition. The diamond deposition was carried out using the tungsten filament chemical vapour deposition method. Raman spectra have shown that the quality of the diamond deposited on the etched substrate was better than that on the as-polished substrate. The facet size of the diamond film surface on the as-polished substrate was smaller than that on the etched specimen. These effects were caused by the atomic-scale interaction of Co atoms in the binder phase. A special feature of the diamond film on the as-polished specimen was a very rough diamond film surface. This phenomenon was observed to result from the abnormal movement of the Co-rich binder phase to the deposited diamond particle surface and the subsequent non-uniform growth of particles during deposition. The phenomenological characteristics of the Co-rich binder phase movement were also explained.