Abstract: Forming milling cutter is used to mill large modulus gears, and the fitting accuracy of its blade type directly affects the accuracy of the machined tooth surface. Aiming at the problem of low precision of gear tooth profile machined by forming milling cutter, a method of high precision fitting of helical gear milling cutter edge shape by small segment NURBS is proposed. Based on the principle of gear meshing, the mathematical model of helical gear tooth surface is established by MATLAB. The contact line and tool edge point of helical gear milling are obtained by coordinate transformation. The traditional single arc fitting, piecewise cubic fitting and small piecewise NURBS fitting are carried out on the edge point to obtain different precision tool edge types. In order to verify the machining accuracy of small piecewise NURBS fitting edge, VERICUT is used to form milling of different precision edge tools, and compared with the standard helical gear profile. The research shows that the precision of the machined tooth surface is improved by the small segmented NURBS fitting edge tool.