The　failure　process　of　TiN　coating　was　studied　by　micro-scratch　and　scanning　electron　microscope,　the　mechanism　of　friction　coefficient　fluctuation　was　analyzed　and　the　fracture　toughness　of　the　coating　was　evaluated.　The　results　show　that　at　low　load　stage,　the　TiN　coating　undergoes　shear　slip,　and　the　edge　of　the　scratch　track　appears　from　the　reverse　V-shaped　crack　to　the　parallel　crack,　and　then　to　the　forward　V-shaped　crack;　as　the　normal　load　increases,　the　TiN　coating　undergoes　stepwise　spalling.　Fluctuations　in　the　coefficient　of　friction　are　mainly　due　to　surface　topography　and　coating　failure,　different　loading　methods　have　different　friction　coefficients.　The　fracture　toughness　of　the　TiN　coating　can　be　tested　accurately　with　micro-scratches,　which　is　consistent　with　the　test　results　of　the　indentation　fracture　method　and　the　finite　element　simulation　method.　©　2020,　Acta　Metrologica　Sinica　Press.　All　right　reserved.