Coated tool has characteristics as high surface hardness,good abrasion performance, stable chemical properties,small friction factor and lowerthermal conductivity,etc.The cutting performance is 30% higher than non-coated tool.Promote grade 0.5-1 of processing accurancy. Prolong the gun drill's service life and lower 20%-50%of tool's consumption cost.The normal coating contains TiN,TiAn titanium based coating and AICrN chromium based coating,etc.