1. An “S” shaped detection test piece for comprehensively detecting the precision of the 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 the projections of which in the base plane cross each other and have open and close angle states formed at the intersection, the motion path of the included angle between said ruled surface 6 and the base plane 3 along the “S” shaped line varies unevenly.