The original objects dealt with in laser planar cutting are numerous curve segments out of order, while the processing itself is sequential. The key of auto programming for laser planar cutting is how to convert such curve segments to ordered cutting traces and generate numerical control (NC) codes at last. According to the characteristics of laser planar cutting, the key technologies of auto-programming are discussed and the solutions to every key steps are given here. NC programs of laser planar cutting can be automatically generated from unordered curve segments through such key steps, namely “auto extraction of traces”, “auto analysis of relations between traces”, “auto creation of laser-on points” and “auto plan of the shortest path”.