According to the measurement at grinding stage, we put forward a method based on numerical control machine tools(NC) to measure profile of large aspheric optic. First, we calibrate the straightness of the machine tool sliding guide which is a critical component of the test system and has a function of supporting and orienting, to improve the motion precision of that machine; and second, measure profile of large aspheric optic with the help of NC machine and Heidenhai(MT60); and third, process the test data to further enhance the precision of measurement.