Graphite flake is an electromagnetic interference material of importance for IR screening. In this study, an attempt to improve the performance of graphite flake by coating it with nano-silica using cyclomix (Hosokawa) and hybridizer (Nara) processes was made. Uncoated and coated graphite flakes were examined by scanning electron microscopy (SEM). It was shown that a more uniform coating was obtained using the hybridizer process. Coated graphite flake with a mass ratio of nano-silica equal to 5.25% exhibited the best hydrophobic properties. The test chamber experiments demonstrated that the deposition velocity of coated graphite flake decreased from 0.227cms(-1) to 0.187cms(-1) and its IR interference performance was improved, compared with uncoated graphite flake. The obtained results showed that the coatings on the graphite flake powder with hydrophobic nano-silica enhanced the moisture resistance and electromagnetic interference performance of the graphite flake.