Abstract: The minimum distance between two free-form surfaces is widely used in selecting the cutter diameter and detecting interference during NC machining of complex part. A "contest" procedure is adopted to select the units to be copied, while two special units are reserved in new population, thus the diversified variety of colony is always kept, this makes it possible to approach the global optimal value rapidly with less number of units. The implement shows that the minimum distance between two surfaces can be obtained more quickly and reliably in comparison with the Standard Genetic Algorithm.