The invention belongs to the technical field of micro cutter machining, and provides a side-edge-relief-angle-free micro PCD milling cutter cutting force modeling method which mainly comprises the steps: S1, establishing a cutter coordinate system; s2, defining an infinitesimal radial force dFrj, an infinitesimal tangential force dFtj and an infinitesimal axial force dFaj of a point P on the cutting edge of the cutter at any moment and a radial grinding force dFnj and a tangential grinding force dFfj of a rear cutter surface; s3, determining a cut-in angle and a cut-out angle of a milling cutter; s4, establishing infinitesimal cutting force expressions of the milling cutter in the X, Y and Z directions under the rectangular coordinate system; s5, determining the contact state of the cutting edge and the workpiece; s6, obtaining cutting force models of the milling cutter in the X, Y and Z directions through numerical integration. The model can predict the cutting force of the milling cutter under different main shaft rotating speeds, feeding speeds and radial cutting depths, and then the main shaft rotating speeds, the feeding speeds and the radial cutting depths can be optimized, so that the purposes of reducing cutter abrasion and improving the machining efficiency and the machining quality are achieved.