Abstract: The gear shaping cutter interference of non-standard tooth ring is always a difficult problem in the design and processing of internal teeth. The interference of the tool can be obtained in advance through the simulation of the shaping process, which provides a basis for the optimal design of tooth shape and the design of the shaping cutter. In this paper, two-dimensional contour Boolean subtraction algorithm and cutter interference calculation algorithm are studied. The above algorithm is implemented in C++ builder. The simulation system of internal gear shaping is developed. The graphical simulation of the shaping process and the calculation of cutter interference are realized. The algorithm has been applied and verified in practical production.