Cut-in disrepair of milling inserts are closely related to dynamic equation of cut-in contact. According to the problem of serious cut-in disrepair, dynamic equation of cut-in contact for the waved-edge milling insert with 3D complex groove is studied. Rake face function of 3D complex groove waved-edge milling inserts is founded. Rake face equation of 3D complex groove inserts is founded. Rake face motion equation of 3D complex groove inserts is deduced. Appearance equation of workpiece machining region is deduced. Contact line (LM) equation is deduced, which is the contact line between rake face and workpiece cut-in side surface when rake face moving. Intersection line (C1D1) equation is deduced, which is the intersection line of cutting surface and side surface of workpiece. All the production above are the theory foundation for further researching the relationship between the cut-in style and cut-in disrepair, cut-in style optimization, 3D complex groove insert optimization.