Overlay key, method for forming overlay key and method for measuring overlay precision

The embodiment of the invention discloses an overlay key. The overlay key comprises at least two overlay markers, each overlay marker is provided with a first sub marker and a second sub marker which are centrosymmetric to each other, and each first sub marker and each second sub marker each comprises two strip-shaped patterns which are perpendicular to each other and provided with a common end. At least two overlay markers are located on different layers. The invention further discloses a method for forming the overlay key and a method for measuring the overlay precision.