A novel methodology based on partial differential equation (PDE) was presented in this paper because the existing tool path generation methods for pocket machining cannot meet the requirements of high speed machining(HSM). First, a PDE was introduced by a twodimensional steadystate temperature equilibrium equation. The boundary of the pocket was offset by a tool radius as the boundary of the PDE, and the boundary condition was assigned to zero, based on which a toolpath generation model was established. Then the inner region was divided into the triangle mesh, and finite element method (FEM) was introduced to solve the PDE. Therefore, the isometric curves was obtained from the solution of the PDE. Finally, the isometric curves were connected to generate the spiral tool path. An experimental implementation was conducted to prove the validity of the proposed method. The results show that the proposed method can apparently improve the movements of the machine tool with higher efficiency.