An　electron-emission　theoretical　model　integrating　the　change　in　the　grain　size　of　nanocrystalline　cubic　boron　nitride　(c-BN)　thin　films　was　established.　To　understand　better　the　essence　of　field　emission,　an　accurate　numerical　scheme,　the　transfer　matrix　method,　that　can　be　used　to　compute　the　tunneling　coefficients　of　the　actual　surface　barrier,　was　also　adopted.　The　present　results　show　that　the　emission　current　from　nanocrystalline　grain　films　is　far　larger　than　that　from　regular　grain　films　or　bulk　c-BN.　©　2003　Elsevier　Ltd.　All　rights　reserved.