In this study a pulsed magnetic treatment (PMT) was attempted to improve the cutting performance of the TiCN–Al2O3–TiN/cemented carbides inserts and the effects of the strength of the pulsed magnetic field on the cutting forces, tool wear, the machined surface roughness and mechanical properties were investigated. It is found that the cutting performances of the coated tools are successfully enhanced after the treatment and both the resultant force and the component force for the treated tools are considerably lower than that for the untreated one. In particular, a maximum reduction of approximately 6% in the resultant cutting force is achieved, along with a maximum reduction of 23.8% in the wear area of the flank surface after the treatment. However, the roughness of the machine surface generally shows an increasing trend with the increasing strength of the pulsed field and an increase of approximately 17.6% in the surface roughness is obtained. The hardness from the nanoindentation test indicates an approximately 23% increase after the PMT. The improvements in the cutting and mechanical performances of the coated tool are attributed to the residual stress change caused by the comprehensive effects of the reduction in the defects density within the coating and the phase transformation and magnetostriction of the cobalt within the substrate induced by the field treatment.