In this research KP-4, one of the plastic mold steels, was coated with the AlTiN from one layer to four layers by the PVD method in the $Phi$ cemented carbide ball end mill. Coated KP-4 was processed with various conditions. For example, slope of $15^{circ}$, $30^{circ}$ and $45^{circ}$ the spindle rotation speed was changed from 10,000rpm to 16,000rpm, the tool feeding speed was changed from 1,300mm/min to 1,700mm/min, the depth of cut was also changed from 0.3mm to 0.9mm, and etc. Cutting component force according to the coating layer number, surface roughness, and the wear of tool were studied.