This paper discusses the basic principle of numerical control interpolation, including the straight line and arc (Agreeable circle or Negative circle) interpolation method of point by point comparison, Digital Differential Analyzer (DDA) and time-slicing method. By using Visual Basic 6.0 software, the implementation of the interpolation process and dynamic simulation results are displayed on the screen, and the implementation process of interpolation is observed directly, such as continuous interpolation, manual interpolation, step interpolation and interpolation of a closed graph.