Three-dimensional porous carbon materials with conformal dielectric coatings have great potential to be used for 3D dielectric capacitors or for 3D interpenetrated micro-batteries if the dielectric film is also an ionic conductor. Exploring methods to build a continuous and conformal insulated thin film on porous carbon materials has been highly desired. However, due to their complicated structures, achieving this well-defined insulating layer is very challenging and only few studies have reported but mostly on planar carbon materials. In our study, carbon film composed of carbon nanofibers which was synthesized via electrospinning method were used as substrate to conduct the dielectric layer coating via electrodeposition techniques. Using an ionic liquid (1-Butyl-1methylpyrrolidinium dicyanamide) as the electrolyte and the monomer source, conformal dielectric thin film on the porous carbon sheet was produced which was proved by the extension of their working voltage window from below 3 to 10 V in an ionic liquid electrolyte. In addition, by adjusting the parameters of the electrodeposition, the properties of the dielectric layer could be tuned, which is reflected on the change of their electrochemical performances. The properties of this dielectric thin layer will be presented.