1. An “S” shaped detection test piece for comprehensively detecting a precision of a numerical control milling machine, characterized in that, said test piece consists of an “S” shaped ruled surface equal thickness edge strip and a rectangular base, respectively forming two “S” shaped curves in two different planes and projections of which in a base plane cross each other and have open and close angle states formed at an intersection, and a motion path of an included angle between said ruled surface and the base plane along the “S” shaped line varies unevenly.