A methood for APT program verification by means of plotting CLFILE data is suggested. This system enables an APT programmer to verify APT programs by multicolor line. It is an experimental software system that transforms CLFILE data generated from an APT IV(A4V3) source program into the desired form depicting tool path, and plots the data for the APT program verification. Especially, the 3D sculptured surfaces are considered and the system can be used for 3-and 5-axis NC programming.